Synchronous state counter

ABSTRACT

A synchronous state counter, which is responsive to an incrementing pulse for incrementing the state of the counter, is provided with a plurality of latches which output a binary representation of the number stored in the counter. Each latch is provided with a circuit for altering a state of the latch in response to a control signal. The control signal for the latch storing the least significant bit of the number is provided by the incrementing pulse. The control signals for the latches storing bits more significant than the least significant bit of the number is provided by a plurality of circuits responsive to the incrementing pulse and to the state of each latch supplying a bit less significant than the bit stored in the particular latch being controlled.

BACKGROUND OF THE INVENTION

Electronic calculator systems of the type wherein all of the main electronic functions are integrated in a single large cell integrated semiconductor chip or in a small number of such chips, are described in the following U.S. Patents, which are assigned the assignee of this invention:

U.S. Pat. No. 3,919,532 issued to Michael J. Cochran and Charles P. Grant on Nov. 11, 1975 and entitled "CALCULATOR SYSTEM HAVING AN EXCHANGE DATA MEMORY REGISTER".

U.S. Pat. No. 3,934,233 issued to Roger J. Fisher and Gerald D. Rogers on Jan. 20, 1976 and entitled "READ-ONLY-MEMORY FOR ELECTRONIC CALCULATOR".

U.S. Pat. No. 3,931,507 issued Jan. 6, 1976 to George L. Brantingham entitled "POWER-UP CLEAR IN AN ELECTRONIC DIGITAL CALCULATOR".

The concepts of these prior applications have made possible vast reductions in the cost of small personal-size calculators. Continuing efforts to reduce the cost of these products include the design of a single chip calculator system for use in large capacity calculators, such as scientific or business calculators. The chip disclosed herein may be utilized in scientific or business calculators for instance, because this chip has provisions for a number of storage registers, in addition to operational registers, as well as sufficient capacity to solve the more complicated mathematical expressions and functions used in scientific and business calculators including, for example, trigonometric and logarithmic relationships.

The present invention relates to a synchronous state counter of the type which may be used in an electronic calculator or microprocessor. An entire electronic calculator system, including the synchronous state counter of this invention, is disclosed. The electronic calculator disclosed is a serial, word organized calculator; however, it will be evident that the invention disclosed is not limited to that type calculator system. In the prior art, the state time counters were provided by, for instance, push/pull matrices of the type disclosed in U.S. Pat. No. 3,919,532. The push/pull matrix is preferably used with the sequentially addressed memory system or a shift register and provides an individual signal for each of the possible state times of the system. Thus for a calculator having 32 state times, for instance, 32 eight state time outputs would be provided by the state time generator of the prior art.

It is one object of this invention to provide a state counter which was not dependent upon a bit being shifted through either a sequentially addressed memory or a shift register. It is another object of this invention to provide a state counter providing the state outputs in binary format. It is yet another object of this invention to provide a synchronous state counter of simplified design, It is still yet another object of this invention to provide a synchronous state counter of expandable design.

The foregoing objects are achieved according to the present invention as is now described. In a preferred embodiment of the invention, a synchronous state counter is provided on electronic calculator semiconductor chip for providing a binary indication of which one of the possible state times an electronic calculator is operating in. The state counter is responsive to an incrementing pulse provided once ech state time by the electronic calculator system. The state counter includes a plurality of latches for providing a binary representation of the number stored in the counter and a circuit associated with each one of the the latches for independently altering the state of the latch in response to a control signal. The control signal for the latch associated with the least significant bit of the number is provided by the incrementing pulse. The control signals for the latches storing bits more significantly than the least significant bit of the number are provided by control circuits responsive to the incrementing pulse and to the state of all latches storing bits less significant than the bit stored in the latch being controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objects and advantages thereof, will be best understood by reference to the following detailed description of an illustrative embodiment when the read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a pictorial view of the portable, electronic, hand-held calculator of the type which may embody the present invention;

FIG. 2 is a functional schematic diagram of a single chip calculator system of the type which may embody the present invention;

FIG. 3 depicts a functional block diagram of the single chip calculator system embodying the present invention;

FIGS. 4(a) and 4(b) depict the timing signals generated by a clock implemented in the calculator system, the timing signals being shown in representative form;

FIGS. 5(a) and 5(b) depict a segmented display and a manner in which a calculator system may be interconnected therewith;

FIGS. 6(a) and 6(b) depict the format of the data word stored in the operational and storage registers of the calculator system, the MASK codes which are used in the instruction words implemented in the read-only-memory and how these various masks relate to the data words;

FIGS. 7(a)-7(c) form a logic diagram of the program counter, the branch logic, the test circuitry, the subroutine stack and the read-only-memory of the calculator system;

FIGS. 8(a)- 8(i) form a logic diagram of the instruction word decoder logic; the operational registers, the storage registers, the register address buffer, and the counter associated with the storage registers;

FIG. 9 is a logic diagram of the operational register selector gates;

FIGS. 1d(a)-10(d) form a logic diagram of the arithmetic unit and the R5 register;

FIGS. 11(a)-11(f) form a logic diagram of segment/keyboard scan and scan generator counter, keyboard logic, display decoder, output register and state time generator;

FIGS. 12(a)-12(g) depict the format of various instruction words described in Table I;

FIG. 13 is a logic diagram of circuits used to interconnect the test circuitry of FIG. 7 with the K1-K4 keyboard line pins of FIG. 11; and

FIG. 14 depicts alternate embodiments of register architecture for the operational and storage registers of the system.

DETAIL DESCRIPTION OF SPECIFIC EMBODIMENT

Referring to FIG. 1, an electronic portable calculator the type which may employ features of this invention is shown in pictorial form. The calculator 1 comprises the keyboard 2 and the display 3. The display 3, in one embodiment, consists of twelve digits or characters, each provided by an array of light-emitting diodes, a vacuum fluorescent tube, liquid crystal devices or other display means. The display is preferably implemented having eight mantissa digits, two exponent digits, and two annotator places for signs, et cetera (one place for the mantissa and one place for the exponent), thereby permitting outputting of data in scientific notation. Ordinarily, the display would be of the seven segment or eight segment variety, with provision for indicating a decimal point for each digit. The keyboard 2 or other such input means preferably includes a set of number keys (0-9), a decimal point key, a plurality of function command keys including, for example, exponential, logarithm and trigonometrical functions. The exponential and logarithmic function command keys include, for example, X², the square root of X, the reciprocal of X, e^(X), the common log of X, and the natural log of X. The trigonometrical functions include for instance the sine, cosine, tangent and their inverses, the hyperbolic sine, hyperbolic cosine, and hyperbolic tangent of X and inverse hyperbolic functions. Other function command keys include store (STO), and recall (RCL), keys for respectively storing and recalling a number stored in one of the memory or storage registers implemented on the chip. The enter exponent key (EE) allows exponent entry of the number displayed in scientific notation. A plus/minus key is provided for changing the sign of the display number. An exchange key (X:Y) is provided for exchanging operator and operand of an arithmetic function. More conventional function command keys are supplied, including the clear key (C), the clear entry key (CE), and the plus (+), minus (-), multiply (×), divide (÷), and equal (=) keys.

Referring now to FIG. 2 there is shown a functional schematic diagram of the single chip calculator system. A single chip 10 is shown here in a standard twenty-eight pin dual-in-line package; however, it is to be understood that how the chip 10 is shown as being interconnected with a twelve-character display 11 utilizing a segment scan technique. Each of the 7 segments of the character plus the decimal point for each character position are individually connected in common to the segment scan conductors 14. An individual common lead for each character position is connected by bus 15 to chip 10. The details of segment scanning are explained with reference to FIGS. 3 and 5 and it should be evident to one trained in the art that the number of segments selected and the number of characters selected is a design choice.

Chip 10 is interconnected with an X/Y metrix keyboard 12 utilizing five column conductors 16' and eight row conductors 14', the row conductors 14' being individually connected to the segment scan conductors 14 and the column conductors 16' being individually connected via bus 16 to chip 10. An X/Y matrix keyboard having five column conductors 16' and eight row conductors 14' may accommodate up to 40 switches located at the intersections of the conductors; however, the number of conductors 14' and 16' and consequently the number of switches is a design choice. The chip 10 is further connected to a source of DC electrical power through a common connection (Vss) at pin 1, a Vdd connection at pin 2, and a V_(DISP) connection at pin 3 for the display. Further, a resistor 13 is connected between pins 28 and 1 as a means of controlling the chip's oscillator frequency. External resistor 13 could of course be implemented on chip 10, however, resistor 13 is preferably implemented off chip 10 in order to be able to "fine tune" the frequency of the clock oscillator implemented on chip 10.

Referring now to FIG. 3 there is shown a functional block diagram of the single chip calculator system of this invention showing various circuits implemented on chip 10. A detailed description of the individual function blocks will be discussed subsequently with regard to FIGS. 7, 8, 9, 10 and 11, with only a general functional description of the basic system here set forth. It is to be understood that on the block diagram of FIG. 3, a connection represented by a single line may represent a plurality of actual hardware interconnections, and for ease and simplicity of illustration, a single line may represent a plurality of different functions. The calculator system of this invention includes on chip 10 a main program read-only-memory (ROM) 30, preferably having two sections which may be referred to as ROM A and ROM B. The reason for denoting that ROM 30 has two sections will be subsequently explained in regard to the instruction words implementable in ROM 30. Main program ROM 30 is responsive to an eleven bit ROM address (A₁₀ -A₀) stored in program counter 32a and produces, in response thereto, a thirteen bit instruction word (I₁₂ -I₀), which is provided to instruction word decoder logic 31. Instruction word decoder logic 31 interprets the instruction word received from ROM 30 and produces in response thereto a plurality of command signals to the other circuits implemented on chip 10. These command signals direct how data is transferred within chip 10, how the data is manipulated by arithmetic unit 40 and serves several other functions which will be explained with reference to the circuits receiving the command signals.

Program counter circuit 32a includes an add-one circuit and is associated with branch logic 32b. The add-one circuit in program counter 32a increments the ROM address stored in the address register in program counter 32a by adding the number one to the address stored in the address register during each instruction cycle, thereby causing the instruction words stored in ROM 30 to be read out sequentially. At time, however, it is advantageous to be able to execute the same instruction word repetitively and therefore the add-one circuit in program counter 32a is responsive to a HOLD command which disables the add-one circuit allowing the address stored in program counter 32a to remain unchanged. Branch logic 32b is responsive to commands generated by instruction word decoder logic 31 for inserting a new ROM address in program counter 32a, thereby permitting the program stored in ROM 30 to "branch" to a new location in ROM 30 rather than cycling sequentially through the instruction words stored in ROM 30. As will be seen with respect to the discussion of the instruction word set and the details of the branch logic 32b and program counter 32a circuits, a branch instruction received from instruction word decoder logic 31 may be either a conditional or an unconditional branch. If unconditional, the branch automatically occurs. If conditional, however, the branch instruction is executed only if the state of the condition latch 41 matches the state of a selected bit in the conditional branch instruction. If a match does not occur, program counter 32a merely cycles to the next sequential ROM address. Thus, branch logic 32b and program counter 32a circuits are interfaced with condition latch 41.

If a branch is to be accomplished, the program counter must be updated with the new ROM address by branch logic 32b. This new ROM address is typically derived from the branch instruction, but as will be seen from the discussion regarding the instruction word set, the new ROM address may also be derived from an address stored in an auxiliary register called R5 register 34. Since R5 register 34 can be loaded with an address corresponding the depression of a particular switch or key on keyboard matrix 12 (FIG. 2) or with number from an operational register 38 supplied via arithmetic unit 40, the new ROM address can be made dependent on the particular keyboard key depressed or can be an "indirect" address generated in one of the operational registers.

Branch logic and program counter circuit 32 is further interconnected with a subroutine stack 33. Subroutine stack 33 is preferably a three level stack having eleven bits per level which receives an incremented ROM address from program counter 32a in response to an unconditional branch command (CALL) and supplies the most recently received ROM address back to program counter 32a in response to a RETURN command received from instruction word decoder logic 31. The ROM address loaded into subroutine stack 33 in response to an unconditional branch command is the incremented address to which program counter 32awould have otherwise cycled. Therefore, when an unconditional branch instruction is encountered in ROM 30, program counter 32a is caused to branch to the address specified by the unconditional branch command and then increments that address by one each instruction cycle until another branch or a return command is received. When a return command is encountered, the most recently stored address in subroutine stack 33 is loaded back into program counter 32a, thus the addressing of the program stored in ROM 30 "returns" to the instruction address following the last unconditional branch instruction word location. Since subroutine stack 33 is a three level stack, three levels of subroutining are possible. Should a fourth address be loaded into subroutine stack 33, the first stored address is lost and only the second through fourth addresses will remain in subroutines stack 33.

R5 register 34 is an eight bit register which stores the two least significant digits generated by arithmetic unit 40 unless keyboard logic 35 in combination with a keyboard scan circuit in the scan generator/counter 36 indicates that one of the calculator keyboard keys has been depressed, in which case, an address associated with the key depressed is loaded into R5 register 34. The keyboard key address loaded into R5 register 34 may then be loaded into program counter 32a upon a "Branch on R5" instruction command, thereby permitting the keyboard to address ROM 30. Alternatively, a "branch on R5" instruction command may be utilized to perform indirect addressing by using the contents of one or two of the operational registers 38, as aforementioned. Since program counter 32a is an eleven bit counter, the three most significant bits (MSB's ) are loaded with zeros when the eight bit address from R5 register 34 is loaded into program counter 32a.

Referring briefly to FIG. 6a, the format of the data stored in the various operational and storage registers implemented on chip 10 is depicted along with the effect of the various mask codes used in many instruction words. With respect to the format of the data, it can be seen that there are sixteen digits (DO-D15) in a data word; preferably, the three most significant digits (MSD's ) provide twelve flag bits and the thirteen least significant digits (LSD's ) provide thirteen digits for numeric data. However, as will be seen, the calculator system disclosed has sufficient flexibility to permit the three MSD's to be used either partially or totally for data storage in addition to the thirteen LSD's, if desired during certain operations. Whether the calculator is operating in hexadecimal or binary coded deciman (BCD) four binary bits are required to represent each digit. The data word is serially organized, so each data word comprises 64 (e.g. 16 × 4) binary bits.

Referring again to FIG. 3, chip 10 is provided with four operational registers (register A-d) 38 and sixteen data storage registers (X_(X) -X₇ and Y_(O) -Y₇) 39. The operational registers 38 and the storage registers 39 are each 64 bit shift registers, accommodating the 64 bit format of the data words. The sixteen data storage registers 39 are separated into X and Y groups, each group comprising eight serially connected registers, thus each group of eight registers may be viewed as a 512 (e.g. 64 × 8) bit shift register. Both groups of shift registers are interconnected with storage register input-output (I/O) circuit 42. The first bit clocked out of a storage register 39 is the least significant bit of digit DO.

The operational registers 38 are similarly 64 bit registers, the 38a portion having sixty bits of capacity and the 38b portions having four bits of capacity. The operational registers 38, including the point of junction between 38a and 38b portions, are interconnected with a plurality of register selector gates 43 which control the exchange of data between the operational registers and with arithmetic unit 40. As will be subsequently discussed in greater detail, the separation of operational registers A-D 38 into the aforementioned sixty bit and four bit portions and the connection therebetween with register selector gates 43, facilitates right or left shifting of data, because then it is desirable for the register selector gates 43 to be able to selectively pick off the data word starting with the D15 digit, which is stored in portion 38b or the DO digit, which is stored in portion 38a at the beginning of an instruction cycle (state S0) for instance. Storage register I/O circuit 42 is interconnected with register A to permit movement of a data word between a selected storage register 39 and operational register A.

A data word may be either outputted from Register A 38 and stored in a selected storage register and stored in REgister A. To effect such movement of a data word between Register A and a selected storage register 39, an appropriate instruction workd from ROM 30 is received by instruction word decoder logic 31 indicating (1) from which group, X or Y, the particular storage register 39 is to be selected and (2) whether the data word is being moved from Register A to a storage register or from a storage register to Register A. The contents of an address register, register address buffer (RAB) 44, indicates which one of the eight storage registers in the addressed group is being selected.

RAB 44 is a three bit address register which can be loaded either from R5 register (three least significant bits) or from three selected bits of an instruction word as directed by appropriate instruction commands. The data words stored in the eight storage registers 39 in each group normally recirculate, with each 64 bit data word moving to an adjacent storage register location during each instruction cycle. Thus, during one instruction cycle the contents of X₀ shifts to X₁ while the contents of X₁ shifts to X₂ and so forth. This shifting, of course, is responsive to the outputs from clock 45. Storage register I/O circuit 42 further includes a three bit counter which is likewise responsive to clock generator 45 for indicating which one of the eight data words stored in the addressed group is ready to be read out of X₇ or Y₇. Thus the three bit counter implemented in storage register I/O circuit 42 increments by one each instruction cycle. When a data word is to be read from or into a selected storage register 39, RAB 44 is first loaded with a three bit binary number indicating which one of the eight data word locations in a group is to be addressed. Then an instruction word is decoded by instruction word decoder logic 31 commanding storage register I/O circuit 42 to select the proper group, X or Y, and to count instruction cycles until the counter contained therein matches the state of RAB 44. Thus it can be seen that it could require up to seven instruction cycles for the selected data word in one of the groups, X or Y, to be shifted into a position preparatory to reading out of or into that group. Thus storage register I/O circuit 42 generates the HOLD command which inhibits incrementing program counter 32 until the counter in storage register I/O circuit 42 matches the state of RAB 44 and the desired data is moved between the appropriate group and Register A.

Arithmetic unit 40 is a serially organized arithmetic unit which includes a binary coded decimal (BCD) corrector. The BCD corrector may be disabled by an appropriate instruction command thereby permitting arithmetic unit 40 to operate either in hexadecimal base or in binary coded decimal base, as desired. As forementiond, the data format preferably includes twelve flag bits. These flag bits are used, for instance, during many problems for keeping tract of the results of certain logical operations. Including the flag bits in the data words stored in the operational registers 38A and 38B and in the storage registers 39 is an important feature of this invention which permits greater programming flexibility in implementing the instruction words into ROM 30 and further simplifies chip 10 in that it eliminates the need for the discrete or dedicated flag registers or latches used in the prior art, and permits the flags to be processed in arithmetic unit 40 rather than in separate flag logic circuitry as done in the prior art. Arithmetic unit 40 is responsiveto selected flag bits and selected instruction commands (Table I, Section 7) for setting the condition latch 41. Thus, in accordance with selected instruction words (Table I, Section 7), the twelve flags may be individually set, reset, toggled, or tested. Further, the three MSD's used for flags may be arithmetically operated upon in hexadecimal using appropriate instruction words (see Table I) with appropriate flag masks (see FIG. 6).

The "set flag" instruction (see Table I, Section 7) loads a binary one into the addressed flag bit, while the "reset flag" instruction loads a zero; and "toggle" changes a zero flag to one or a one flag to a zero. The "flag test" instruction causes the condition latch (COND) to be set only if the tested flag has been previously set, e.g., contains a binary one. Thus the flag bits can be advantageously used to determine whether or not a conditional branch instruction will cause a branch to occur.

Register A and Register B are outputted to display decoder 46 in response to a display instruction command. The contents of Register A contains the digits to be displayed by the display 11 (FIG. 2) and Register B is loaded wih bits which indicate the position of the decimal point and whether or not a particular digit is to be blanked. By using Register B to store digit blanking and non-blanking codes along with a decimal point and negative signal codes, which codes are loaded into Register B in accordance with instruction words contained in ROM 30, is another important feature of this invention eliminating the need for using disrete leading zero blanking circuitry, as used in the prior art. The display decoder 46 is connected to output register 47 which provides the digit scan lines to the display 11 via lines 15. The scan generator 36, display decoder 46 and output register 47 cooperate to drive the display 11 (FIG. 2) using the segment scan display technique disclosed by U.S. Pat. application Ser. No. 565,489 filed Apr. 7, 1975 and assigned to the assignee of this invention.

Referring now to FIGS. 4a and 4b, there is shown, in representative form, the timing signals generated by the clock generators 45 implemented on chip 10. The clock generators 45 may be of conventional design, and are not shown in detail herein. The clock generators sequentially generate φ1, P1, φ2 and P2 clock pulses, each pulse having a pulse width time of approximately 0.625 microsecond in this embodiment. The precise frequency of the clock generator is typically "fine tuned" using an external resistor 13 (FIG. 2). A full sequence of the four above-identified clock pulses comprise one state time (S0, S1, S2, etc.), each state time having a duration of approximately 2.5 microseconds in this embodiment. One state time represents the time needed for two bits of a data word to be clocked out of a register. Thus, it requires two state times for a four bit hexadecimal or BCD numeral to be inputted into the arithmetic unit 40 from an operational register 28. Since sixteen digits in all comprise one data word (as is shown in FIG. 6), thirty-two state times (S0-S31) are required to output all sixteen digits from a register. Thus, thirty-two state times (S0-S31) represent one instruction cycle, as is depicted in FIG. 4b, and an instruction cycle has a duration of approximately 80 microseconds in this embodiment. The state times are generated by state time generator 48.

As will subsequently be discussed, the clock is responsive to a decoded display instruction for slowing the speed of the clock during display operations. During display operation, the period of a state time is ten microseconds and the period of an instruction cycle is 320 microseconds.

In addition, clock pulses may be provided at every P₁ and P₂ time which are simply labeled P and other clock pulses are provided at every φ1 and φ2 time, which are simply labeled φ, as is shown in FIG. 4a. Further, clock pulses are provided at selected P or φ times in selected state times (for instance S1.φ2), as is also exemplified in FIG. 4a.

Referring now to FIGS. 5a and 5b, there is shown diagramatically in FIG. 5a the ten decimal digits, 0-9, displayable by a seven segment character display along with an eighth segment used as a decimal point. With respect to FIG. 5b, the seven character segments are labeled A-G and the decimal point segment is labeled P. For each character position there is a common cathode 9 provided for the eight segments, as is shown in FIG. 5b. The eight segments A-G and P for each character position are respectively connected in common by segment conductors S_(A) -S_(G) and S_(P). Chip 10 uses segment scanning according to the method disclosed by U.S. Pat. No. 4,014,012, which issued Mar. 22, 1977 wherein the segments are scanned sequentially and the digit cathodes are selectively energized in conjunction with the scanning of the segment electrodes to form the characters 0 - 9 and a decimal point. By using the segment scanning method of U.S. Pat. No. 4,014,012, the segment amplifiers generally used heretofore in the prior art are eliminated. Thus, chip 10 may be directly interconnected with display 11.

Referring again to FIG. 3, scan generator counter 36 sequentially energizes the S_(A) - S_(G) and S_(G) and S_(P) conductors (FIG. 5b) via lines 14 and pins SEG A - SEG G and SEG P (FIG. 11). Output register 47 is loaded each time a different segment is scanned with a twelve bit binary code indicating whether the cathodes 9 (FIG. 5b), associated with each of the twelve character positions, should be energized via lines 15 and pins D1 - D12 (FIG. 11) permitting the scanned segment in the corresponding character positions to actuate.

Referring again to FIG. 6a, there is shown the format of the data word stored in operational registers 38A and 38B and storage registers 39 (FIG. 3). As aforementioned, each data word comprises sixteen digits of serial data, each digit comprising four serial bits. Thus, an entire data word comprises 64 (e.g., 16 × 4) bits. The three most significant digits of the data word preferably comprise the twelve flag bits and the thirteen remaining digits comprise numerical data, the first eleven digits thereof preferably being the mantissa and the least significant two digits being the exponent.

As aforementioned, associating the twelve flag bits with the thirteen digits of numeric data in one data word storage location is an important feature of this invention which eliminates the need for separate flag registers.

In FIG. 6b there is shown the mask codes which are incorporated in many of the instruction words implemented in ROM 30; the set of instruction words storable in ROM 30 and decodable by instruction word decoder logic 31 (FIG. 3) are described in TABLE I. The set of instruction words stored in ROM 30 in this embodiment are listed in TABLE IV. As can be seen from TABLE I, a mask field code (MF) is used in many of the possible instruction words. The mask field denotes to the register selector gates 43 (FIG. 3) which digits of the sixteen digit data words are to be passed to the arithmetic unit 40 (FIG. 3) and which digits are to be recirculated. The mask codes are needed, because it is often desirable to perform some arithmetic or flag logic operation on only the mantissa or only the exponent or both the mantissa and the exponent or on a particular flag bit or perhaps the whole data word. As can be seen from FIG. 6b, there are twelve masks, having codes 0000 through 1011, which are listed and are associated with a rectangle beneath a representation of a sixteen-digit data word. The digits enclosed by the rectangle associated with a particular mask are permitted (by the mask decoder logic 200 (FIG. 8) in instruction word decoder logic 31 when the associated mask code is received) to pass through arithmetic unit 40 while those digits outside the rectangle are recirculated via gates 316a-d (FIG. 9). As will be seen with respect to the detailed discussion of the mask logic (FIG. 8), the mask codes cause the register selector gates 43 (FIGS. 3 and 9) to operate in timed relation with the data being outputted from an operational register 38 in accordance with the state times indicated by state time generator 48 (FIG. 3). The masks of FIG. 6b operate on complete digits, but certain individual bits may be selected by further mask arrangements as will be explained henceforth.

Referring now to FIG. 12, TABLE I, there are shown the set of possible instruction words stored in ROM 30, decoded by instruction word decoder logic 31 and utilized by the remainder of the system. TABLE I refers to FIG. 12 for drawings representative of the various types of instructions. As can be seen, the instruction word comprises thirteen binary bits (I₁₂ - I₀). A thirteen bit instruction word length provides for the possibility of having up to 2¹³ or approximately 8,000 different instruction codes; however, it will soon be evident that not all these possible instructions are used. Looking first to the first two instructions, namely the "branch on condition" and the "branch unconditionally" instructions, it will be seen that there is a 1 in the I₁₂ position. Since all remaining instructions use a 0 in the I₁₂ position, it will be seen that there are approximately 4,000 variations of the first two instructions. The "branch unconditionally" instruction has a zero in the I₁₁ position following the one in the I₁₂ position and an address in the I₁₀ - I₀ positions. Since the "branch unconditionally" address contains 11 bits and since the program counter 32a contains 11 bits, the "branch unconditionally" instruction can cause the branch anywhere within ROM 30, including branches between ROM A and ROM B. The "branch on condition" instruction, on the other hand, contains only a ten bit address because the I₁₀ bit is used as a condition bit. If the state of the condition bit (I₁₀) matches the state of the condition latch, the branch will occur; if there is no match, the branch instruction is ignored. There being only ten bits in the address for the "branch on condition" instruction, when the branch is executed only the last ten significant bits are loaded into the eleven bit address register of program counter 32a. The most significant bit in the program counter remains unchanged. Since a zero in the most significant bit (A₁₀) in the program counter addresses only those instruction words in that part of ROM 30 denoted as ROM A, and a one in the most significant bit (A₁₀) in the program counter addresses only those instruction words located in that portion of ROM 30 denoted as ROM B, the "branch on condition" construction only permits branching within the confines of either ROM A or ROM B. The unconditional branch instruction may also be considered a "CALL" instruction inasmuch as an incremented address (the location following the location of the unconditional branch instruction) is stored in the subroutine stock 33 if the branch is accomplished.

The next listed instruction words in TABLE I, namely "Branch to R 5" and "Return" will be discussed subsequently.

Referring to part five of TABLE I, the operations under mask control contain a zero in the I₁₂ position, the mask field code in the I₁₁ - I₈ positions, and an operational code in the I₇ - I₀ positions. The operational code is divided into two bit J, three bit K, two bit L, and one bit N fields, as shown in TABLE I. For certain special operations the L and N fields are combined into one three bit field (LN field). TABLE I explains in detail the operations performed in response to particular binary codes entered into the aforementioned J, K, L, and N fields.

Remembering that the mask field, i.e., I₁₁ - I₈ has only 12 possible mask codes 0000-0101, 0111-1010, 1101 and 1111, while a four bit binary number has sixteen possible codes associated therewith, then there are four codes which may be loaded into the mask field position, namely 0110, 1011, 1100 and 1110, which will not be decoded as a mask operation. Two of these four codes, 1110 and 1100, are decoded by instruction word decoder logic 31. The 1110 code is referred to as the miscellaneous non-mask code; the family of instruction words using the miscellaneous non-mask code are explained in Part 6 of TABLE I. The miscellaneous non-mask operations have a four bit Q and four bit P fields in addition to the zero and the I₁₂ position and the 1110 in the I₁₁ - I₈ positions. In this instruction set, the Q field is ignored by decoder logic 31 unless specifically referred to in this instruction set; the P field is decoded to perform the operations indicated, which are generally operations not making use of the arithmetic unit 40. Thus, these operations relate to transforming data between the storage registers and the operational registers, storing three bit codes in RAB 44 (FIG. 3), storing the contents of R5 register 34 (FIG. 3) in the program counter 32a, or enabling or disabling the BCD corrector in arithmetic unit 40.

The "Return" instruction (Section 4 of TABLE I) and "Branch to R5" location (Section 3 of TABLE I) may be considered as part of the miscellaneous non-mask code since these two instructions also have a 1110 in their I₁₁ - I₈ positions. The Return instruction causes a branch to the address most recently stored in subroutine stack 33.

Other non-mask operations include the flag operations which are defined by a 1100 in the mask field MF. The flag operations are explained in detail in Part 7 of TABLE I. Although generally referred to as a non-mask operation, the flag operations may be thought of as very detailed mask operation in the calculator disclosed, because a specific flag bit in a data word is examined or operated upon rather than merely operating on a particular one or set of digits using the normal mask codes defined in FIG. 6. Flag operations have not heretofore been thought of as being similar to mask operations, since the flags have been typically stored in special registers of latches separate from the numeric data.

DETAILED DESCRIPTION OF SYSTEM LOGIC DIAGRAM

The various parts of the system of FIG. 3 will now be described with reference to FIGS. 7, 8, 9, 10, 11 and 13 which depict in detail the logic circuit implemented on chip 10 to form the circuits depicted by the block diagrams of FIG. 3. The following discussion with reference to FIGS. 7 - 11 will refer to the logic signals available at many points on chip 10. It should be remembered that a logical zero corresponds to a negative voltage, that is, V_(dd), while a logical one refers to a zero voltage, that is, V_(ss). It should further be remembered that the P-channel MOS transistors depicted in FIGS. 7-11 become conductive when a logical 0, i.e, a negative voltage, is applied at their respective gates. When a logic signal is referred to which is unbarred, i.e., has no bar across the top of it, the logic signal is to be interpreted as "true" logic; that is, a binary one indicates the presence of the signal (Vss) whereas the binary zero indicates a lack of the signal (Vdd). Local signal names including a bar across the top thereof are in "false" logic; that is, a binary 0 (Vdd voltage) indicates the presence of the signal wheras a binary 1 (Vssvoltage) indicates that the signal is not present. FIGS. 7 - 11 do not depict the clock generators implemented on chip 10, the clocks generating clock pulses φ₁, P₁, φ₁, P₂, in accordance with the clocking signals depicted in FIG. 4a. The clock generators are of conventional design and are responsive to decoded display instruction command signal for decreasing the frequency of the clock, as aforementioned.

THE ROM AND PROGRAM COUNTER

Referring now to FIG. 7, there is shown the logic diagram of the program counter 32a, the branch logic 32b, subroutine stack 33, condition latch 41, test logic, and ROM 30 along the interconnecting circuitry. The details of ROM 30 are not shown in detail in FIG. 7, however, ROM 30 is of the virtual ground type disclosed in U.S. Pat. No. 3,934,233 by Roger J. Fisher granted Jan. 20, 1976. Using the virtual ground read-only-memory of U.S. Pat. No. 3,934,233 permits the size of the ROM to be significantly reduced in comparison with the ROM's typically used in the prior art by using one ground or V_(ss) line for five or more P difusions. Lines A₀ - A₁₀ supply, in parallel, at time S22.φ1, the eleven bit address for addressing ROM 30. Address lines A₀ - A₆ address the X address decoder disclosed in U.S. Pat. No. 3,934,233 while address lines A₇ - A₁₀ address the Y address decoder of U.S. Pat. No. 3,034,233. Lines I₁₂ - I₀ provide, in parallel, the instruction word corresponding to the address appearing on address lines A₀ - A₁₀. The false logic instruction word is clocked out of ROM 30 at S29.φ2 by gates 111 and inverted to true logic by inverters 110. Address lines A₁₀ - A₀ are loaded from program counter 32a at S22.φ1 by gates 112, unless the power up clear latch 162 has inserted a logical one into complex gate 113, which in turn inhibits conduction by gates 112. The power incorporated in clock 45 and comprises a latch which preferentically enters a first state for generating the logical one to complex gate 113 when power is initially applied to the system. The state of the latch changes when the clock turns on sufficiently to change a capacitor associated with the reset input to the latch.

Gates 114 unconditionally precharge address lines A₀ -A₁₀ to Vdd at S21.φ2 of each instruction cycle and when power up-clear logic finally inserts a zero into complex gate 113, the address previously received by ROM 30 is 00000000000₂. Thus, power up-clear logic effectively forces the ROM to branch to the very first location contained therein. This automatic branch to 000₁₆ using the ROM precharge gates 114 in combination with gates 113 is an important feature of this invention which permits the operational registers 38 and storage registor 39 along with the remaining logic circuitry to be prepared for numeric operations in accordance with instruction words loaded into ROM 30 beginning at location 000₁₆ rather than using dedicated circuitry therefore or requiring an address to be jammed into program counter 32a after the state of the PUC signal changes.

Program counter 32a comprises an eleven bit shift register, having twenty-two inverter stages 115 and gates 116 for precharging the stages, for forming an address register. A serial input to program counter 32a is received on line 117 and a serial output is communicated via line 118 to add-one circuit 119. Gates 143 interconnect the eleven stages of program counter 32a in series. Add-one circuit 119 is a simplified serial add-one circuit comprising a NAND gate 119a, one input of which is connected to line 118 and an output of which is connected to inverter 119b. The output from inverter 119b is communicated to another input of NAND gate 119a, to the gate electrode of transistor 119c and the source electrode of transistor 119d. Line 118 is further connected to the source electrode of transistor 119c and the gate electrode of transistor 119d. The drain electrodes of transistors 119c and 119d are connected together and normally provide the previous eleven bit program counter address incremented by the number one on line 120. The junction between the output of NAND gate 119a and the input of inverter 119b is further interconnected with the HOLD signal generated by gate 500 (FIG. 11) and gate 291 (FIG. 8) to inhibit incrementing the previous program counter address by add-one circuit 119.

The output from add-one circuit 119 normally recirculates via line 120 and gate 121 back to the input of program counter 32a on line 117. Gate 121 is responsive to the output from NAND gate 130 and is normally conductive except when inhibited by a RETURN or KB BRANCH (Branch to R5) commands. Program counter 32a may also be loaded with either ten or eleven bits of the instruction word appearing at gates 110 via lines 122 and gates 123 and 124. When a conditional branch instruction word is decoded and branch logic 32b determines that the condition has been satisfied, the new branch address is loaded from the I₀ - I₉ bits of the instruction word into the A₀ - A₉ bits of program counter 32a via lines 122 and gates 123. When an unconditional branch instruction word (CALL) is decoded, gate 124 is caused to conduct at the same time as gates 123, thereby inserting eleven bits from the instruction word (I₀ - I₁₀) into program counter 32a. The ten or eleven bits from the instruction word are loaded into program counter 32a after the prior ROM address plus one has recirculated serially via lines 117, 120 and gate 121.

THE SUBROUTINE STACK

The subroutine stack 33 is a three-level stack of eleven bit shift registers 33a, 33b, and 33c, each comprised of twenty-two inverter stages 125. Except when subroutine stack 33 is either outputting a return address to program counter 32a or receiving an address from program counter 32a, the eleven bit addresses stored therein are recirculated via gates 126. Gates 126 normally receive a logical zero (i.e., are made conductive) from NAND gate 137, which provides a logical one output only upon receiving either a RETURN signal from NAND gate 135 or a CALL signal from NAND gate 136.

When an unconditional branch instruction is decoded by branch logic 32b, the CALL signal goes to zero permitting the present ROM address plus one to be loaded into subroutine stack register 33a via line 120 and gate 127 from add-one circuit 119. Addresses previously loaded into subroutine stack/registers 33a and 33b are shifted to registers 33b and 33c, respectively, by gates 128. Gates 127 and 128 are responsive to the CALL signal. If an address had previously been loaded into subroutine stack register 33c, it would have been lost upon the execution of another unconditional branch instruction.

Upon the decoding of a "Return" (RTN) instruction by decoder 214 (FIG. 8), the RETURN signal from NAND gate 135 goes to logical zero, thereby causing the output of NAND gate 130 to become a logical one, interrupting the normal insertion of an up-dated address via line 120 when gate 121 becomes nonconductive and forcing the contents of subroutine stack register 33a to be inserted into program counter 32a via gate 129 and line 117. Gates 132 cause the contents of subroutine stack register 33b to be inserted into register 33a and the contents of register 33c to be inserted into register 33b upon the execution of a return instruction. Gates 131 are responsive to the RETURN signal from NAND gate 135.

THE BRANCH LOGIC AND CONDITION LATCH

Branch logic 32B and condition latch 41 cooperate to control gates 123 and 124 in program counter 32a for inserting the address portion of a branch instruction word into program counter 32a. NAND gates 132 form the latch circuit of the condition latch 41 and are responsive to an ADDER COND SET signal from gate 401 (FIG. 10) and a LOAD R5 signal from decoder 508c (FIG. 11) for letting the latch. The latch is reset by either a Return or by such instruction, as is explained subsequently. Complex gates 133 are responsive to COND and COND signals produced by NAND gates 132, a PREG signal from NAND gate 146 and the I₁₀, I₁₀, I₁₁ and I₁₂ bits which are derived from ROM 30, the I₁₀ bit via inverter 134. OR gates 133a and 133b both provide a logical one output only when the state of the condition bit matches the state of the I₁₀ bit. Thus, the output from OR gates 133a and 133b along the I₁₂ and I₁₁ bits and the PREG signals are supplied to AND gate 133c which provides a logical one output only when (1) I₁₁ and I₁₂ indicates that a conditional branch instruction has been outputted from ROM 30, (2) the state of the I₁₀ bit and COND match and (3) PREG is a logical one indicating that the PREG test circuitry is not activated. The test circuitry and the PREG and TIRG signals associated therewith are described subsequently.

NAND gate 136 is responsive to the I₁₂ and the I₁₁ bits and to PREG thereby providing a CALL signal to NAND gates 137 and 138 and to gates 127 and 128 unless the test circuitry has been activated. NAND gate 135 is responsive to the RTN signal from decoder 214a (FIG. 8) via inverter 159 and to the PREG signal for generating the RETURN signal which is a logical zero if (1) a "return" instruction has been decoded and (2) the PREG test circuitry has not been activated.

NAND gate 138 is responsive to CALL from NAND gate 136 and to TIRG for generating a CALL signal which is normally a logical zero unless (1) an unconditional branch (call) instruction has been decoded or (2) the test circuitry has been activated. NAND gate 139a, which normally receives an S20.P1 clock signal via gate 149 in addition to the CALL signal from NAND gate 138, provides a CALL signal at S20.P1 to complex gates 139b. NAND gate 139a is responsive to an S30.P1 clock signal in gate 150 in lieu of the S20.P1 signal if the test circuitry is activated. Complex gates 139b output the CALL signal at S21.φ1 to gate 124, unless the test circuitry is activated, in which case the CALL signal is supplied to gate 124 at S31.φ1. OR gate 133d is responsive to the output from AND gate 133c and to CALL from NAND gate 138, thereby producing a logical one output upon the occurrence of either: (1) a condition/I₁₀ match on a condition branch instruction, or (2) the CALL signal (on an unconditional branch instruction or PREG test mode operation). The output of OR gate 133d is supplied to NAND gate 133e along with a normal S20.P1 signal from gate 149 (or S30.P1 during TRIG test operation). NAND gate 133e, in conjunction with gates 140, provide a BRANCH signal at S21.φ1 (S30.P1 in test mode) to gates 123 for inserting the I₀ -I₉ bits of the instruction word into program counter 32a.

Inverter 142 outputs a RETURN signal from the RTN signal received from decoder 214a (FIG. 8). Gates 141 are responsive to the I₁₂ branch bit, the RETURN signal from inverter 142 and the S20.φ1 signal fro resetting the condition latch 141 upon the occurrence of either (1) a branch instruction (e.g., I₁₂ = 1) or (2) upon a "return" instruction.

Considering now the timing of the addressing operations of program counter 32a during normal operations, the address stored in program counter 32a is incremented in add-one circuit 119. The incremented address is circulated back into the program counter 32a during S2-S12.φ1 when gates 143 in program counter 32a are clocked. Thus, the incremented address in program counter 32a is updated by state time S12 of an instruction cycle and will normally be clocked into ROM 30 at the following S22.φ1 by gates 112 for reading out the next instruction word. If a conditional BRANCH (and the condition is satisfied) operation is indicated by the present instruction word read from ROM 30 (at the previous S29.φ2), the present address in program counter 32a is still incremented by add-one circuit 119 during S2-S12, but the address portion of the BRANCH Instruction word is jammed into program counter 32a by the action gates 123 and 124 at S21.φ1, thereby inserting a new address one state time before the new address is to be clocked at S22.φ1 into ROM 30. This one state time is sufficient to precharge and conditionally discharge the inverters 115 making up the stages of program counter 32a. During a CALL operation, the incremented address is stored in the subroutine register 33a, and a new address from the I₀ -I₁₀ bit of the CALL instruction word is clocked into program register 32a, a manner similar to the inputting of a BRANCH address.

THE TEST CIRCUITRY

NAND gate 146 is responsive to TEST and K1 signals which are clocked on S31.φ1 to provide at its output PREG. NAND gate 147 is likewise responsive to TEST and K1 but is clocked at S0.φ1 to provide TRIG which is inverted to TRIG by inverter 148. PREG is generated when a ROM address is desired to be inputted directly to program counter 32a via keyboard line L1 for test purposes. TRIG is also generated if the instruction word at the aforementioned address is desired to be serially readout of the chip on line K2 during test operations. The output from inverter 148 is supplied to gate 149 which supplies the S20.P1 clock signal to NAND gates 133e and 139a, the S20.P1 clock signal being the clock signal used during non-TIRG test operations. The TIRG signal, besides being applied as an input to NAND gate 138 is also supplied to gate 150 for supplying the S30.P1 clock signal to NAND gates 139a and 133e, the S30.P1 clock signal being provided during TIRG test operations. PREG is inverted by inverter 151 whose output is connected to gate 145, which is in line 117. Gate 145 is conductive, except during test mode operations, normally permitting the incremented address to recirculate on line 117. Thus, gate 145 inhibits the incremented address outputted from add-one circuit 119 from being inserted into program counter 32a during test mode operations. Instead, the address to be inserted on line 117 during test mode operations is received from keyboard line K1 (FIG. 11) via gate 152 which is responsive to PREG. The output from program counter 32a is supplied to keyboard line K2 (FIG. 11) via line 118, inverter 153 and gates 601 and 602 (FIG. 13). K2 receives, as it will be subsequently shown, the I₀ -I₁₀ bits of the instruction word addressed in ROM 30 during state times S2-S12 of TRIG test mode operations. Accordingly, the output from program counter 32a on line 118 is clocked at S2-S12 to inverter 153 via gate 154. The I₁₁ and I₁₂ bits of the instruction word are also outputted to K2, these bits being outputted during S13 and S14 via gates 155 and 156, respectively, which provide the I₁₁ and I₁₂ bits to the input of inverter 153.

As will be shown, the aforementioned PREG and TIRG test circuitry permits the instruction words implemented ROM 30 to be read out of the chip on line K2 according to addresses inserted into the chip via line K1 when the calculator has been put into a test mode via input signals which are discussed with reference to FIG. 13. Once in the PREG test mode, an address may be inserted into program counter 32a from K1 via gate 152. This insertion would be timed to be inserted into program counter 32a in the same manner as an updated address from add-one circuit 119. Any branching which might occur at the same time a PREG test operation address is inserted into program counter 32a (according to the previously addressed instruction word) is inhibited by the PREG inputs to AND gate 133c and NAND gate 136. Thus, as the old address is shifting out of the program counter 32a on line 118, an externally supplied address is being inputted from K1 via gate and 152 and line 117 during the same instruction cycle. The incremented address is blocked by the action gate 145. This externally supplied address is then used to address ROM 30 at the following S22.φ1.

If the chip is also placed into the TIRG test mode (in addition to PREG), the I₀ -I₁₀ bits of the instruction word are clocked into program counter 32a via gates 124 and 123 at S31.φ1, it being remembered that the CALL S21φ1 and BRANCH S21.φ1 signals are automatically activated at S31φ1 during TIRG test mode operations. The I₀ -I₁₀ bits instruction word are then shifted out of program counter 32a at (S2-S12), φ1 via line 118, gate 154 and inverter 153. At the same time a new address is inputted from K1 via gate 152. Thus, during each instruction cycle, an external source may be used to address ROM 30 and the code contained in ROM 30 at that address is read out via K2, the I₀ -I₁₀ bits being provided by program counter 32a and the I₁₁ and I₁₂ bits being provided by gates 155 and 156. It should be evident that the entire contents of the ROM 30 may be checked in approximately 2,000 instruction cycles whereas if the contents of ROM 30 were to be checked by requiring the calculator to perform all possible instructions, it should be evident that that technique would require significantly more than 2,000 instruction cycles.

Additionally, the state of the condition latch 41 is outputted as COND to keyboard line K3 (FIG. 11) via an inverter 160, responsive to latch 41, and gates 605-608 (FIG. 13). Similarly, HOLD is outputted to keyboard line K3 during test mode operations via gates 605, 607 and 608 (FIG. 13).

Referring now to FIG. 13, there is shown the test logic associated with keyboard lines K1-K4. The K1-K4 pins depicted in FIG. 13 are the same pins as the K1-K4 pins depicted in FIG. 11. The address received on line K1 is directly connected to the input to gate 152 (FIG. 7). The instruction word received from the ROM is outputted via gates 601 and 602 to pad K2. Gates 603 and 604, which are responsive to TEST AND TEST, respectively, isolate the instruction word output from line K2 except during test operations.

Pin K4 is responsive to a Vdd signal for producing the TEST signal. Pin K4 supplies one input to NOR gate 609. The other input to NOR gate 609 is derived from S28.φ1. The output from NOR gate 609 is supplied through an inverter 610 and gate 611 to NAND gate 612. The other input of NAND 612 is responsive to the power up clear signal, PUC. The output of NAND gate 612 provides the TEST signal and via inverter 613 the TEST signal.

Pin K3 is responsive to the HOLD and COND signals produced by the calculator when in a test mode. Accordingly the HOLD and COND signals are provided via gates 605 and 606, respectively, clocked at state times S3 and S2, respectively, to a gte 604 which is responsive to TEST. The output from gate 607 drives a gate 608 for providing a signal to pin K3 during test operations indicative of HOLD and COND.

THE INSTRUCTION WORD DECODER LOGIC

The instruction word decoder logic 31 is shown in FIG. 8. Referring now to FIG. 8, a decoder 200, which decodes the mask portion of instruction field, receives from inverters 110 (FIG. 7) the mask field (MF) of the instruction word, i.e., bits I₁₁ -I₈, and their complements I₁₁ -I₈. Decoder 200 is also responsive to the B-E (and complements B-E) outputs from state time generator 68 (FIG. 11), which provides a binary representation of which one of the 32 state times this system is operating in. Since there are sixteen digits in a data word and since the first digit, (DO) starts imputting at S₀, then the second digit begins inputting at S₂ and so on. Decoder 200 decodes the aforementioned bits to produce the masks MANT, LLSD, etc (FIG. 6b). In addition, decoder 200 decodes the I₁₂ bit, thereby disabling decoder 200 when I₁₂ is a logical zero (I₁₂ is a logical one then), when a condition or unconditional branch instruction has been outputted from ROM 30 (FIG. 7). Decoder 200 decodes the twelve mask codes which are explained with reference to FIG. 6. Remembering that a mask code indicates which bits of a data word are to be operated on by arithmetic unit 40 and which are to be merely recirculated by register selector gates 43, it is desirable that when a particular madk field has been decoded by decoder 200 that a mask signal be generated during the state times at which the particular digit of a word is to be operated on by arithmetic unit 40 in accordance with the mask codes defined in FIG. 6. Therefore, decoder 200 is responsive not only to the MF field (bits I₁₁ -I₈ of the instruction word), but also to the binary representation of which one of the 32 state times the system is operating in. Since the digits are outputted only at even state times, as aforementioned, decoder 200 need not be responsive to the least significant bit from state time generator 48 on line A or A.

Decoder 201, which is associated with decoder 200, is responsive to the I₁₁ -I₈ bits of the instruction word and their complements, I₁₁ -I₈ and in addition the I₁₂ bit to disable the decoder 201 when a conditional or unconditional branch instruction has been outputted from ROM 30 (FIG. 7). Decoder 201 decodes the miscellaneous (MISC) and flag operation (FLGOP) codes which also occupy the MF field, as is explained with reference to TABLE I, Sections 6 and 7. As will be seen, the outputs from decoder 201, MISC (via inverter 203) and FLGOP (as well as FLGOP via inverter 211), are applied as inputs into several other decoders for disabling or enabling signals during miscellaneous or flag operations.

Decoder 210 receives bits I₀ -I₃ and their complements I₀ -I₃ of the instruction word and it is enabled only during miscellaneous operations by MISC which is derived from decoder 201 via inverter 203. Decoder 210 decodes the stack instructions (STAY, STAX, STYA, AND STXA) and the address buffer instruction (NAB and RAB), which are explained in TABLE I, Section 6.

Decoders 204 and 205 decode the bit and digit defining bits, respectively, for the flag instructions (see TABLE I, Section 7, B and D fields). Decoder 204 is responsive to the A and A state time from state time generator 48 (FIG. 11), φ1 and φ2 clock pulses (which are applied to separate loads 204a and 204b associated with decoder 204) and the flag bit defining bits I₂ - I₃ of the B field of the flag instruction (see TABLE I, Section 7). The I₂ -I₃ bits define which bit of four in a digit is selected and decoder 204 provides enabling signal when there is a match between (1) the bit selected and (2) the time at which that bit enters arithmetic unit 40 as denied by the P1 and P2 clocks and by whether the state time is odd or even as defined by state time A. Decoder 205 decodes the digit selected (as defined by bits I₄ -I₅ of the flag instruction, see TABLE I, Section 7). and is responsive to the B-E and B-E outputs from state time generator 48 (FIG. 11) for generating an enabling signal when there is a match between (1) the digit selected and (2) the time at which that digit enters arithmetic unit 40. The output from decoder 204 is nanded in decoder 216 onto line 213 and the output from decoder 205 is nanded in decoder 216 onto line 217. Lines 213 and 217 are applied to NAND gate 207 whose output is connected to input of NOR gate 212. The other input of NOR gate 212 is FLGOP from decoder 201 and thus NOR gate 212 provides a logical one output upon the decoding of flag operation instruction during the time that the bit selected in decoder 204 within the digit selected in decoder 205 is outputted from the operational registers 38 into arithmetic unit 40. The output from the mask field decoder 200 is applied to decoder 202 for performing a NAND operation thereby providing an output on line 218 of a logical zero except when (1) a mask operation has been decoded and (2) the state time counter 48 indicates that the selected bits are to be inputted to arithmetic unit 40. The outputs of NOR gates 212 and 218 are applied to the inputs of NOR gate 219 which outputs a logical one except during either (1) arithmetic mask operations decoded by decoder 200, or (2) flag bit mask operations decoded by decoders 204 and 205. It should be appreciated that the arithmetic masks and flag masks are generated slightly ahead of the time the selected digit or bit is outputted from an operational register to provide sufficient time for the MOS gates to be actuated. The output from NOR gate 219 is outputted through a series of gates 220 providing a signal MSK φ which is outputted to the arithmetic unit one φ time before the corresponding data is inputted to the adder. The output from NOR gate 219 is also inverted by an inverter 222 to provide a MASK φ signal to mask delay generator 225, NAND gate 230, and gate 223, inverter 250 and gate 251.

A mask delay generator 225, whose function is more fully described with respect to the operational register selector gates 43, comprises a series of clocked inverters for providing a delayed mask signal in both true and false logic, the MD φ/P signal being two state times behind the MASK φ signal provided by inverter 222. The MDφ signal is one φ time earlier than the normal MD φ/P signal and an MDP signal is provided which provides a P clock during the occurrence of an MDφ/P signal.

Decoder 215 is responsive to the FLGOP signal and the I₀ -I₅ bits (and their complements) of the instruction word for decoding the STORE signal (see TABLE I, Section 3, the LN field), the SHIFT signal, the IR5 signal and the 2R5 signal (see TABLE I, Section 5, K field). Decoder 206 is responsive to the MISC signal and the I₀ -I₂ bits instruction word for generating the BCDS and BCDR signals, which are indicative of whether the arithmetic unit is to BCD correct (see TABLE I, Secion 6). These signals are applied to separate NAND gates 228 and 229 which are arranged as a latch. The output from this latch is the HEX signal which is indicative of whether the adder is to add in hexidecimal or is to BCD correct.

Decoder 208 is generally responsive to selected I₀ -I₄ bits of the instruction word and provides a T/T output and a K → Y output. The T/T signal is generated during flag operations when a flag is to be tested or toggled while the K → Y signal is generated during non flag operations when the number one is desired to be loaded into the least significant masked digit position in the Y input of arithmetic unit 40. The K → Y signal is inverted by inverter 252 and applied to one input of AND gate 251. AND gate 251 is also responsive to the MASK φ signal from inverter 222 and to a delayed MASK φ signal supplied by inverter 250. Thus, upon occurrence of a K → Y signal and a MASK φ signal, AND gate 251 is effective for inserting a one into the least significant bit of the least significant digit immediately following the beginning of the MASK φ signal. The T/T signal, as will subsequently be seen, is also used to insert a one into the appropriate bit position in the Y input to arithmetic unit 40; thus the T/T is inverted by inverter 224 and applied as an input to NOR gate 226. The other input to NOR gate 226 is from the output of AND gate 251. NOR gate 226 drives a series of gates 231 which are effective for inserting the aforementioned one into the appropriate bit position in the Y input to the arithmetic unit 40.

Decoder 209 decodes the BRK signal which causes a branch to occur in branch logic 32b, the branch location being defined by the contents of R5 register 34 (FIG. 10). Referring again to FIG. 7, the BKR signal is supplied as an input to NAND gate 130 interrupting the normal address recirculation path via lines 120 and 117 for the updated address. BKR also closes gate 157 for inserting the contents of R5 register 34 via inverter 158 onto line 117 for insertion into program counter 32a via gate 145. Returning to FIG. 8, NAND gate 209a generates the S/RS signal which is generated during flag operations for setting or resetting a flag and the DISP signal which is generated during display operations.

Decoder 214 is responsive to the I₇ -I₀ bits of the instruction word and to FLGOP, FLGOP, and MISC signals for generating the signals used to operate the various register selector gates and register recirculation gates. Decoder section 214a generates the RTN (return) signal which is supplied to inverter 142 and to NAND gate 135 (FIG. 7). Decoder section 214b generates AX-DX signals and section 214c generates AY-DY signals, which are inverted by inverters 221. AX-DX and AY-DY signals are supplied to NAND gates 231a-231d and 232a-232d, respectively, and are indicative of which ones of the operational registers A-D are to be interconnected with the X and Y inputs to the arithmetic unity using the register selector gates 43 (FIG. 9). NAND gates 231a-231d are also responsive to the GMASK signal on line 234 and to the STORE signal generated by decoder 215. NAND gates 232a-232d are also responsive to GMASK signal on line 296. The purpose of the STORE and GMASK signals, in respect to these aforementioned NAND gates, and the timing interactions of these gates with respect to movement data within the various operational registers, between the operational registers and with arithmetic unit via register selector gates 43 will be explained subsequently with reference to FIG. 9. The 214d portion of decoder 214 decodes the I₀ -I₂ bits of the instruction word, those bits corresponding to the L and LN fields in the instruction words control the operations under mask control (Table I, Section 5) for generating the EXCH, Σ→K and Σ→J signals. The Σ→J signal is indicative of a decoded instruction indicating that the results from the arithmetic unit 40 on line Σ' is to go to the register defined by the J field and similarly the Σ→K signal indicates that the results from the arithmetic unit 40 on line Σ' is to go the register defined by the K field, or neither field, in which case a binary 10 occurs in the L field, which is simply not decoded by decoder 214 (See Table I, Section 5). Decoder 214e is responsive to the FLGOP and I₁ and I₀ bits of the instruction word for decoding the TGL (TOGGEL) signal which is used invert a selected flag bit.

The EXCH, Σ→K, Σ→J, TGL, STORE, and S/RS signals are supplied to a decoder 227 whose outputs are supplied to decoder 238 along with the AX-DX and AY-DY signals from inverters 221 and the SR' signal from NOR gate 237. The outputs from decoder 238 are applied as inputs to decoder 239 for decoding the recirculation signals RA, RB, RC, and RD and the adder output signals ΣA, ΣB, ΣC, and ΣD. The RB-RD recirculation signals are inverted to true logic by inverters 236. The RB-RD signals are applied to NOR gates 235b-235d, respectively, along with a RECMASK signal from NAND gate 247 for producing RECB - RECD signals. The recirculation signal RA is supplied to an input of OR gate 244 along with the EXCH' signal derived from decoder 214 via NAND gate 240, which is also responsive to S1. The output of OR gate 244 supplied to a NAND gate 247 via an inverter 248. The output of NAND gate 245 is supplied to NAND gate 246 for producing a RECA signal. NAND gate 246 is also responsive to the LA (Load A) signal from inverter 249 indicating that the contents of one of the storage registers is to be outputted to operational register A.

The ΣA - ΣD outputs from decoder 239 are supplied to NAND gates 233a - 233d, respectively, for generating Σ→A - Σ→D signals which are used to control selector gates 43 for determining to which one of the operational registers A-D the result outputted on line Σ' from arithmetic unit 40 is to be communicated. NAND gates 233a - 233d are also responsive to the MD signal from the output of the mask delay generator on line 253.

The right shift (SR') signal is generated by a NOR gate 237 which is responsive to the SHIFT signal from decoder 215 and to the I₀ bit from the decoded instruction word. The SR' signal, besides being supplied to decoder 238, is also communicated to a NAND gate 230 for supplying an SR signal to register selector gates 43. The SR signal supplied to the register selector gates is under mask control and therefore NAND gate 230 is also responsive to the MASKφ signal from the output of inverter 222. The SR' signal is further communicated to inputs or OR gate 253 via an inverter 254. OR gate 253 is responsive to AND gate 223. AND gate 223 is responsive to a logical zero signal supplied at S 31φ2, to a logical one signal supplied at A1φ2 and to OR gate 294. OR gate 294 is responsive to the output from NOR gate 212 and to the mask signal on line 218. NAND gate 247 is responsive to the output of OR gate 253 and to MDφ/P via line 253 from the output of the mask delay generator 225 for producing the RECMASK signal, which is provided to inverter 248 and NOR gates 235b - 253d.

OR gate 243 is responsive to the MASKφ output of NOR gate 219 and to a SHIFT signal from decoder 214 via inverter 255. The output of OR gate 243 is supplied to AND gate 256 along with MDφ from mask delay generator 225. AND gate 257 is responsive to the output from NAND gate 241, to SHIFT from decoder 215 and to MASKφ from NOR gate 219. The outputs of AND gates 256 and 257 are supplied to NOR gate 259 which drives gate 295 for generating the GMASK signal on line 296 which supplied as an input to NAND gates 231a 231d and 232a - 232d.

NAND gate 241 is responsive to the MDφ/P signal on line 253 and to the EXCH signal from NAND gate 240. OR gate 242 is responsive to the SHIFT signal from decoder 215, the I₀ bit of the instruction word and the MDφ signal from mask delay generator 225. The MDφ signal is generated one φ time before than the normal MDφ/P signal by mask delay generator 225. The output from OR gate 242 and the output from NAND gate 241 are supplied to a NAND gate 260 for generating an SLRC' signal. The SLRC' signal is inverted by inverter 261 and is clocked through a series of gates 262 along with the SLRC' signal for generating the SLRC and SLRC signals on lines 263 and 264, respectively. The SLRC and SLRC signals cooperate with gates 321a - 321d and 320a - 320d, respectively, in the register selector gates 43 (FIG. 9) and with gates 230 and 336a-d to control right or normal shifting of data as is more fully described hereinafter.

The TGL and EXCH' signals from decoder 214d are supplied to a NAND gate 274 for supplying a TGEXCH signal on line 265 to arithmetic unit 40. The load A (LA) signal supplied to inverter 249 is generated as is now explained. AND gate 266 is responsive to the STXA and STYA signals from decoder 210. A NOR gate 267 is responsive to the output from AND gate 266 and to a COMPARE signal from comparison gates 238 for generating the LA signal.

A NAND gate 234 is responsive to the MDφ/P signal on line 253 and to the EXCH' signal from inverter 240 for supplying an EXCH signal under mask control to the appropriate register selector gates 43 (FIG. 9). EXCH' from NAND gate 240 is also supplied via an inverter 268 to NAND gate 269. NAND gate 269 is also responsive to the flag set/reset signal S/RS from NAND gate 209a. NAND gate 269 controls a gate 270 which connects the output of the arithmetic unit 40 on line Σ' with the Σ bus which is interconnected with various register selector gates 43 (FIG. 9) and to the storage registers 39. The S/RS signal is also supplied to a series of gates 271 for inserting a set or reset flag bit (as defined by I₀) via an inverter 272 to register selector gates via a gate 292 which is responsive to the series of gates 271.

NAND GATE 273 is responsive to the STORE signal generated by decoder 215, the I₀ bit of the instruction word and FLGOP from decoder 201 for generating an ADCON signal for arithmetic unit 40. ADCON is a logical one when the arithmetic unit is to add the data or the X and Y inputs and a logical zero when it is to subtract the data on the Y input from the data on the X input.

REGISTER ADDRESS BUFFER

The RAB 44 is a three bit address register shown in FIG. 8, comprising three pairs of inverters 275, the contents of which are normally recycled at S30 via gates 276. RAB 44 is selectively loadable by the I₄ -I₆ bits of an instruction word via gates 277 which are controlled by a series of gates 279 responsive at S31 to a NAB signal received from decoder 210 via inverter 278. RAB 44 is also selectively loadable from the three least significant bits of the number stored in R5 register 34, via gates 280 which are actuated by a series of gates 281 responsive at S31 to a RAB signal from decoder 210 via inverter 282. The output from the three stages of RAB 44 are applied in parallel to the inputs of comparison gates 283 in storage register input/output circuit 42.

STORAGE REGISTER INPUT/OUTPUT CIRCUIT

Storage register input/output circuit 42, shown in FIG. 8, includes a three stage counter 284, each stage of which comprises two inverters, 284a and 284b. The counter is incremented once each instruction cycle by an S29 signal. The output from the three stage counter is applied on lines R, S, and T to comparison gates 283.

Comparison gates 283 output the COMPARE signal which is normally a logical one, a logical zero being outputted only when the state of the three bit counter 284 matches the state of the three bit number in RAB 44. The output of comparison gates 283 is connected to the inputs of four NOR gates 285a-285d. These four NOR gates are separately connected to the STAY, STYA, STAX and STXA signals, respectively, generated by decoder 210 and to the COMPARE signal from comparison gates 283. Thus, the four NOR gates 285a-d normally provide a logical zero output, except that a selected one of the NOR gates 285a-o will provide a logical one output upon the occurrence of (1) the decoding of a storage register operation by PLS 210 and (2) the COMPARE becoming a logical zero indicating a match between the contents of counter 284 and RAB 44. NOR gate 285a being responsive to the STAY and COMPARE signals, normally causes the data in the Y group of storage registers 39 to recirculate via gate 286a but upon receiving a STAY signal plus a COMPARE signal (e.g., both logical zeros), NOR gate 285a causes (via inverter 288a) gate 287a to become conductive and causes gate 286a to become nonconductive, thereby permitting the selected data word in the Y group storage registers to be read out on open circuited line 289a and to be replaced with data being read out of the 38b portion of operational register A into the selected storage location in the Y group via gate 287a. Similarly, NOR gate 285b normally permits recirculation in the X group of storage registers 39 via gate 286b, but allows a data word to be read out of operational register A into the X group via gate 287b which is controlled by inverter 288b which is in turn responsive to NOR gate 285b. NOR gates 285c and 285d are connected to gates 287c and 287d via inverters 288c and 288d, respectively, for providing a path for a data word to be inserted into operational register A from a selected storage register 39.

The STAY, STAX, STYA and STXA signals are also provided to NAND gate 290 which provides a logical 1 to NAND gate 291 when a storage register instruction has been decoded. NAND gate 291 is also responsive to COMPARE, thereby providing a logical zero HOLD signal whenever a storage register instruction has been decoded and there exists a mismatch between RAB 44 and the counter 284. The eight storage registers in each of the X and Y groups of storage registers 39 are conventional shift registers and therefore are not depicted in detail herein.

THE OPERATIONAL REGISTER SELECTOR GATES

Referring now to FIG. 9, there is shown a schematic diagram depicting the operational register selector gates. As can be seen from FIG. 9, the operational register selector gates preferably comprise a plurality of MOS transfer gates generally controlled by logic gates 230-235, 246 and 262.

As previously discussed, the operational registers A-D are divided each into two portions, a 38A portion and a 38B portion. The 38A portion provides sixty bits of storage for storing fifteen four-bit decimal digits. The 38B portions provide four bits of storage for one decimal digit. The stages of operational registers are not shown in detail, although convention 21 stages may be utilized especially if the operational registers are of the architecture depicted in FIG. 13.

At state times S₀, the D₀ -D₁₄ digits of a data word are stored in the 38A portion of an operational register, while the D₁₅ digit is stored in the 38B portion of an operational register. A digit of a data word is clocked in two state times, so at state time S₂ the D₁₅ and D₀ -D₁₃ digits are stored in the 38A portion while the D₁₄ digit is stored in the 38B portion when the data is merely recirculating via gates 316a-316d. As can be seen, there are two outputs from each operational register 38 connecting that register with the X input on line 302 or the Y input on line 303 to the arithmetic unit 40. The normal output is on line 301a-301d via gates 320a-320d and another output is on lines 305a-305d via gates 321a-321d. The outputs from gates 320a-320d and 321a-321d are each respectively connected to a common point 306a-306d before being interconnected by gates 310a-310d and 311a-311d with lines 302 and 303. Gates 320a-320d are responsive to the SLRC signal from line 263 (FIG. 8) while gates 221a-221d are responsive to the SLRC signal from line 264 (FIG. 8). The SLRC signal on line 263 is normally a logical 0, but becomes a logical 1 when a left shift command has been decoded by instruction word decoder logic 31 and the mask delay MD is enabled (e.g., a logical 1) or an exchange operation is indicated and MD is enabled. Thus, gates 320a-320d are normally conducting while 321a-321d are normally nonconducting except during the aforementioned operations. As can be seen, the normal outputs from the operational registers 38 is by lines 301a-301d to common points 306a-306d.

When a data word is not being outputted from an operation register 38, it is recirculated; and even during many outputting operations the data word also recirculates. The normal recirculation path is through gates 316a-316d for operational registers A-D. Gates 316a-316d are responsive to the RECA-RECD signals generated by NAND gate 246 and NOR gates 235b-235d, respectively (FIG. 8). The recirculation gates 316a-316d connect the output of the 38B portions on line 305a-306d with the inputs to the 38A portions on lines 307a-307d.

When an entire data word is outputted to the arithmetic unit 40, the D₀ digit is outputted from the 38A portion while the D₁₅ digit is recirculated via gates 316a-316d to the 38A portion and is subsequently outputted therefrom as the last digit of the data word. Since arithmetic unit 40 has a two state time delay, the D₀ digit from the arithmetic unit is inputted to the 38A portion after the D₁₅ digit has recirculated.

Recalling that during arithmetic operations, shifting operations, and exchange operations either all or a selected portion of the data word stored in an operational register 38 may be operated on according to the indicated operation (the selected portions being operated on is dictated according to the mask field of the decoded instruction word) the operational register selector gates 43 are arranged so as to permit the non-selected portions of the data words to be recirculated while the selected portions are either shifted or read into and out of the arithmetic unit 40 or exchanged as required by the decoded instruction word.

Since the normal output from the operational registers is on lines 301a-301d, the MASKφ signal provided by inverter 222 (FIG. 8), occurs as a selected digit or digits to be operated on under a selected mask (FIG. 6) is outputted from the 38A portion. Actually, MASKφ is provided one φ time early to set up the MOS gates in time. However, because gates 321a-321d control the output from the 38B portion of operational registers A-D during the aforementioned right shift for exchange operations, a digit desired to be unmasked appears at the output of the 38B portion (e.g., the time needed to cycle through the 38B portion) later than it would have been outputted on lines 301a-301d. Thus, mask delay generator 225 (FIG. 8) delays MASKφ two state times providing an MDφ/P signal which is used in controlling gates 246 and 235b-235d by controlling the RECMASK signal applied thereto except during right shift operations.

Considering now right shifting of a data word under mask control, for instance, a right shaft operation to be accomplished under the MANT (FIG. 6) mask of a data word in operational register A, the D₁₅, D₀ and D₁ digits are first recirculated via gate 316a. Then gate 316a is opened and the D₃ digit being outputted from the 38A portion of operational register A is recirculated on line 301a and by gates 230a, 335a, and 336a back to the input of operational register A on line 307a. During this time, the D₂ digit was loaded into the 38B portion and changed to a binary 0000 by gates 308a and 309a and temporarily stored there until it is reinserted into the data word at the most significant digit under mask control at which time gates 335a and 336a are turned off and gate 316a is again turned on. This, it can be seen that all the digits within the MANT mask, that is the D₂ -D₁₂, have been right shifted one digit, the original least significant digit being lost and a 0000 being loaded into the most significant digit. Gates 336a-336d are controlled by the RECMASK signal from NAND gate 230 (FIG. 8) which is responsive to the MASKφ and SR' (right shift) signals. As can be seen, the recirculation gates normally operate on a two state time delay mask, but during right shift operations, must operate on a non-delayed mask. Gates 337a-337d are controlled by the respective register selector logic gates 231a-231d (FIG. 8) which are responsive to the GMASK signal on line 234 (a delayed mask in this case), STORE from decoder 215 (FIG. 8). Gates 308a-309d are responsive to the signals from NAND gates 231a-231d while gates 309a-309d are responsive to the SR signal from NAND gate 230 (FIG. 8).

During a left shift of data in operational A under the MANT mask, for instance, the D₁₅, D₀, and D₁ digits are recirculated by gate 316a. Thus, at the beginning of state time S₆, the D₂ digit is ready to be shifted out of portion 38B of operational register A; at this time the SLRC signal on line 263 (FIG. 8) changes to a binary one at the aforementioned two state times later than the normal MASKφ signal, and the output from the 38B portion is then applied by gates 321a and 310a to the X input of arithmetic unit 40. Recirculation gate 316a is likewise opened two state times later than a normal mask (e.g., MD controls the RECMASK signal generated by NAND gate 247). The output on Σ' line 410 (FIG. 10) from the arithmetic unit 40 is, at the same time, applied by gates 270 (FIG. 8) and 312a to the input of operational register A. Since arithmetic unit 40 has four bits of delay associated therewith and since no data has been inputted to arithmetic unit 40, arithmetic unit 40 subsequently outputs 38a portion of operational register A on line 307a. Since no data is being inputted into the Y input of arithmetic unit 40, arithmetic unit 40 does not alter the data being entered on the X input but merely acts as four bits of delay during a left shift operation. After the most significant digit under mask control is read out of portion 38B, the recirculation mode is re-established by gate 316a and the SLRC signals revert back to a binary zero. Thus, a 0000 is being inserted into the least significant digit under mask control and the most significant digit has been lost, the intervening digits being left shifted one digit.

During the aforementioned left shift operations, it can be seen that gates 310a-310d must be enabled on a mask delayed two state times. However, during normal arithmetic operations when data is being read out on lines 301a-301d, gates 310a-310d and similarly gates 311a-311d (which control inputting of data to the Y input of arithmetic unit 40) must be operable on a normal mask signal or a delayed mask signal, depending on the type of operation being accomplished. Thus, the NAND gates 231a-231d and 232a-232d (FIG. 8) controlling the various selector gates 310a-310d and 311a and 311d are enabled by the GMASK signal on line 234 (FIG. 8) from NAND gate 259 (FIG. 8) on the normal mask for all operations except exchange and left shift when enabled on the delayed mask DMφ/P. The register selector gates 312a-312d, which control the inputting of data words into the operational registers 38 via Σ line 304 and gate 270 (FIG. 8) from the output of arithmetic unit 40 online Σ', are controlled by NAND gates 233a-233d (FIG. 8) which are enabled only on a delayed mask because the result from arithmetic unit 40 on line Σ' is delayed one digit (two state times) due to two-state time delay of arithmetic unit 40. NAND gates 231a-231d are also inhibited by the STORE signal from decoder 209, so that the register receiving the data word, i.e., the register defined by the J field in the instruction word and decoded by decoders 238 and 239 (FIG. 8), is inhibited from entering the arithmetic unit 40. In addition during a store operation the output from one register is applied to the arithmetic unit 40, the output from the other being inhibited by the STORE signal; thus, the adder does not alter the number being inputted and outputs the data word back to the other register, thereby storing the contents of one register in both registers.

Gates 234 (FIG. 8) and gates 314 and 315 are utilized during an exchange operation. Considering an exchange between register A and register B under mask control, the digits normally recirculate via gates 316a14 316d until the delayed mask comes up, at which time gates 321a-d become conductive and recirculation gates 316a and 316b become nonconductive. Gates 321a and 321d are now made conductive because the SLRC signal applied thereto now becomes a logical zero upon the occurrence of an exchange operation and delayed mask signal. The output from register B is then applied by line 305b and gates 321b and 311b to the Y input of the arithmetic unit 40. Gate 338b is controlled by NAND gate 232b by the aforementioned delayed mask GMASK signal on line 234 (FIG. 8). In addition to going to arithmetic unit 40, the contents of operational register B appearing on the Y input to arithmetic unit 40 is communicated back to the A register by gate 315, which is actuated on a delayed mask by NAND gate 234 (FIG. 8). The output from the A register is conveyed by line 305a and gates 321a and 314 to line 304. Line 304 (Σ) is normally connected to the Σ' line of arithmetic unit 401 however, during an exchange operation and the aforementioned flag set and reset operations, line 304 is disconnected from the Σ' line of arithmetic unit 40 by the action of gate 270 (FIG. 8). Line 304 is disconnected from arithmetic unit during an exchange operation, for example, because the data being applied to line 304 from operational register A by gate 314 would otherwise be garbled by the data exiting from arithmetic unit 40. Thus the output from operational register A now on line 346 is conveyed to the input of operational register B via gate 312b. Gate 270 (FIG. 8) is controlled by NAND gate 269 (FIG. 8) which is responsive to the S/RS signal and to EXCH generated by inverter 268 (FIG. 8).

As can be seen, gates 310a-310d control which one of the operational registers A-D is to be applied to the X input of the arithmetic unit 40 on line 302 via common points 306a-306d, respectively, while gates 311a-311d control which one of the operational registers A-D is to be interconnected with the Y input of the arithmetic unit 40 on line 303 via common points 306a-306d, respectively. Similarly, gates 312a-312d permit the interconnection of the output of arithmetic unit 40 on line 304 with any one of the four operational registers A-D. Permitting all the operational registers to be connected to either of the inputs or the output of arithmetic unit 40 is an important feature of the invention permitting greater flexibility in programming the calculator.

It should also be noted that during the aforementioned store and exchange operations that the exchanges and stores may be accomplished under mask control thereby providing more increased flexibility in the programming of the electronic calculator enclosed herein. This novel feature may be advantageously used, for example, when it is desired to use all sixteen digits of a data word during an arithmetic operation. Then, for example, the three most significant digits of the data word (which are normally used for flag storage; see FIG. 6a) may be stored in either another operational register 38 or a storage register 39 and the thirteen digits of data word normally available for arithmetic storage is expanded to sixteen digits for performing arithmetic operations. This is highly advantageous to have more than the usual number of digits of numeric data available during certain calculations to assure that the final result is accurate; that is to say, that to assure that the final result is accurate to ten decimal places, intermediate answers to twelve or thirteen decimal places are occasionally required. The novel selector gate system 43 shown herein permits use of such greater capacity registers during such calculations without the necessity of having such large capacity registers being permanently implemented into the calculator.

ARITHMETIC UNIT

Referring now to FIG. 10, there is shown a schematic diagram depicting the arithmetic unit 40 implemented on chip 10. Arithmetic unit 40 is responsive to the HEX signal from NAND gate 229 (FIG. 8) for indicating whether arithmetic unit 40 is to be operated in binary coded decimal or hexadecimal. The HEX signal is applied to NOR gate 411 along with a logical one from S27 to S1. Thus NOR gate 411 outputs in false logic a HEX signal indicating either that hexidecimal signal BCDR has been decoded in decoder 206 (FIG. 8) or that the data than entering BCD corrector 408 on line 409 then corresponds to flag bits at which time the BCD corrector 408 is automatically disabled from state time S27 through S1. The output from NOR gate 411 is applied to NAND gate 407 for disabling the BCD corrector 408 and NAND gate 406 for disabling illegal BCD code detector.

The adder 405 of arithmetic unit 40 operates on three serial data inputs, 403, 404, and 416. Inputs 403 and 404 correspond to the aforementioned X and Y inputs, which are selectively couplable to the operational registers A-D by the operational registers selector gate 43. The other input, 416, contains a CARRY/BORROW bit from complex gate 417.

ADCON (from NAND gate 273, FIG. 8) provides a SUB signal, via inverter 418 and an ADD signal via another inverter 419. Adder 405 is caused to perform a subtraction function using the two's complement technique. The two's complement is accomplished by inverting each of the bits in the subtrahend and adding a binary one to each digit on line 416 unless a borrow operation was accomplished for the prior digit.

When operating in the addition mode, adder 405 receives the Y input at gate 421 in true logic while gates 422 and 423 receive the Y input in false logic. When the inputs are inverted for two's complement subtraction, however, gate 421 receives the Y input in false logic while gates 422 and 423 receive the Y input in true logic. The conversion between true and false logic and the inversion effected for two's complement subtraction is accomplished by gates 420 and 424 and inverters 425. Gates 420 conduct during two's complement subtraction and are responsive to the ADD signal outputted by inverter 419 while gates 424 are conductive during addition operations and are responsive to the SUB signal outputted by inverter 418.

The output from adder 405 is directed on line 426 to a two stage shift register 415 and thereon by line 409 to one input of BCD corrector 408. A CARRY signal on line 427 from adder 405 is directed to NOR gate 428 and complex gate 402. Complex gate 406 determines whether an illegal BCD digit has been produced during the addition (or two's complement subtraction) of digits being entered adder 405 on lines 403 and 404, and outputs a logical one to NAND gate 428 upon detection of an illegal BCD code (unless disabled by HEX) in register 415. Thus, NOR gate 428 outputs a correct signal which is a logical zero when either a carry signal is on line 427 or the aforementioned illegal BCD code has been detected by complex gate 406. Complex gate 417 is responsive to SUB, ADD, CORRECT, a C/B RESET signal and the C/B RESET signal norred with the carry signal on line 427 by NOR gate 429. The output from complex gate 417 is a logical one if (1) adder 405 is operating in an addition mode, NOR gate 428 indicates that a carry is required and C/B RESET is at zero or (2) adder 405 is operating in a subtraction mode and either a reset or a carry is indicated. During two's complement subtraction a carry indication occurs whenever the subtrahend is smaller than the minuend while a no carry indication indicates that the subtrahend is larger than the minuend, i.e., a borrow must occur and thus a zero is inserted on line 416, thereby not inserting the one normally added to the least significant bit during two's complement subtraction. Thus complex gate 417 produces a logical zero when an add mode and either no carry or a reset is indicated or when in a subtract mode and no reset or no carry are indicated. A reset condition is indicated by a logical one on C/B RESET. C/B RESET is generated by NAND gate 412 which is responsive to SO.φ1 and to the output of NAND gate 413. NAND gate 413 is responsive to MSKφ from inverter 434 and a delayed MSKφ supplied by inverter 414.

Complex gates 430 are responsive to CORRECT, ADD, SUB, the carry signal on line 427, and to A and P1 clocks, determining whether or not an illegal BCD code or carry condition was detected by gate 428 for causing BCD correctpr 408 to add a decimal six for addition or add a ten for subtraction. For example, the addition of decimal numbers X=5 and Y=3 in the adder 405 produces binary output 1000 on line 426 which is a valid 8 in BCD. But adding X=5 and Y=7 produces an output 1100, which is invalid in BCD. Adding six (0110) to 1100 in BCD corrector 408 produces an output on line 410 of 0010. The carry is accomplished by the gates 417, 428 and 406 and the 0010 (a decimal 2) outputted from the BCD corrector 408 is of course the correct result. Since the least significant bit of each digit outputted by adder 405 need not be corrected, the least significant bit enters corrector 408 before complex gate 406 tests at φ 1 of every odd state time for an illegal BCD code.

A binary six or ten is produced by complex gate 430 depending on whether an addition or subtraction operation is performed. The output complex gate 430 is applied to NAND gate 407 for inserting six or ten, as indicated, so long as gate 407 is not disabled by the HEX indicating that hexadecimal arithmetic is required and so long as that adder 405 is operating in the addition mode and a carry is indicated by NOR gate 428 or that adder 405 is operating in a subtraction mode and line 427 indicates that no carry was accomplished. The aforementioned C/B RESET line 436 forces complex gate 417 to insert a one during subtraction operations in the very first bit operated on by adder 405 and inhibits an insertion of a one in the very first bit during addition operations, thereby inhibiting any inaccuracies occurring due to numbers previously existing in arithmetic unit 40 prior to insertion of desired data.

Complex gate 402 is reponsive to SUB, ADD, line 427 and CORRECT thereby producing a one at its output when either (1) gate 428 indicates a carry condition during addition operations or (2) line 427 indicates a borrow condition (no carry) during subtraction operations. The output of complex gate 402 is applied to NAND gate 401, which in turn produces the ADDER CONDITION SET signal to condition latch 41 (FIG. 7).

NAND gate 401 is disabled by C/B STROBE from NOR gate 437 except at the end of a mask operation unless a toggle or exchange operation is indicated in which case NAND gate 401 is disabled by C/B STROBE regardless of the end of a mask operation being encountered. Accordingly, NOR gate 437 is responsive to TGLEXCH from NAND gate 274 (FIG. 8) and to a mask trailing edge circuit 438.

ADDER CONDITION SET is a logical zero when a carry or borrow exists for the first digit after the mask. This indicates an overflow from the mask field for producing an error indication, for instance, or for indicating a desired logical condition, depending on where in a program the overflow occurs. ADDER CONDITION SET therefor also produces a logical zero if a tested flag has been set.

REGISTER R5

R5 Register 34 is depicted in FIG. 10. Register R5 is an eight bit shift register which may be selectively loaded from either the serial output from arithmetic unit 40 on line 410 via gate 467 or may be loaded on lines KR1-3 and KR5-7 via gates 478 from keyboard logic 35 (at which times the MSB of each digit in Register R5 34 is loaded with a zero via gates 479 according to the keyboard code indicated in Table II). Data stored in R5 Register 34 may be selectively loaded into the Y input of arithmetic unit 40 via line 451 and inverter 452, or into program counter 32a (FIG. 7) via inverter 453, line 449 and inverter 158 (FIG. 7) or into RAB 44 via inverter 463. The capability of R5 Register 34 to supply addresses for program counter 32b or RAB 44 is an important feature of this invention providing for indirect addressing of program counter 32b and RAB 44.

R5 Register 34 includes sixteen inverters 454 arranged in eight stages of two inverters 454 each. Each pair of inverters 454 comprising a stage are connected via gates 448 and are connectable via recirculation gates 455, for permitting recirculation of the bit stored in each stage of R5 Register 34. Gates 450 connect the stages to permit shifting of data between the stages of R5 Register 34 in a shift register mode. R5 Register 34 normally operates in the shift register mode, receiving and storing the two least significant digits of the adder output under control of the MDP signal received via NAND gates 461 and 465a unless register R5 34 is loaded on lines KR1-KR3 and KR5-KR7 from keyboard logic 35 in response to a "LOAD R5" signal on line 457. R5 Register 34 also operates in a recirculation mode when a "Branch to R5" instruction has been decoded as denoted by BKR from decoder 209 (FIG. 8). Thus, recirculation gates 455 are controlled by a NAND gate 456 which is responsive to NAND gate 465a, BKR and LOAD R5.

The output from register R5 34 is communicated to the Y input of adder 405 via line 451 when inverter 452 is enabled by a NAND gate 458 and gate 459 and to Branch Logic 32b via line 449. As will be seen, NAND gate 458 and gate 459 are controlled in response to the presence of 1R5 or and 2R5 signals from decoder 215 (FIG. 8). The three least significant bits of R5 Register 34 are loadable into RAB 44 in parallel via inverters 463.

The 1R5 and 2R5 signals are applied to input of two NAND gates 460 and 461. NAND gate 461 is also responsive to a FLGOP signal from inverter 462, to the MDP signal provided by mask delay generator 225 (FIG. 8) and a MD signal generated by inverter 463. Thus the output from NAND gate 461 is normally a logical one, however, a logical zero will occur when upon a MDP signal if 1R5, 2R5, and FLGOP are all a logical one, the zero output occurring for only one P time. A logical zero from NAND gate 461 is communicated through complex gates 464 to latch 465 comprising gates 465a and 465b, setting latch 465 so that the output from gate 465a is a logical one and the output from gate 465b is a logical zero. A logical zero from gate 465b enables gate 466, which in turn enables gate 467, permitting R5 register 34 to function as a shift register and to insert the first eight bits reading out of arithmetic unit 40 on line 402 into R5 Register 34 via gate 467. As will be seen, latch 465 is reset to its normal state with a zero appearing on output of gate 465a and a one appearing on the output of 465b four state times later after R5 Register 34 has been loaded with the two least significant digits outputted on line 402. It should be noted that NAND gate 461 is operated on a delayed mask because the data being outputted on line 431 is two state times behind a normal mask.

NAND gate 468 is responsive to the MSKφ signal from gates 220 received via inverter 434, a delayed MSKφ signal from inverter 469 and the output from NAND gate 460, thus the output from NAND gate 468 is normally a one, but a zero occurs for one P time upon the occurrence of a MSKφ signal and either a 1R5 or 2R5 signal, thus setting latch 465a via gate 464 in much the same manner as NAND gate 461. The latch, now being set, outputs a logical one from gate 465a and a zero at gate 465b, and causes the output from gate 458 to go to a logical zero, NAND gate 458b being responsive to the output from NAND gates 465a and 460. The output from NAND gate 458 enables inverter 452 thereby inserting either 4 or 8 bits of data stored in R5 Register 34 into the Y input of adder 405, the bits being inserted until latch 465 is reset to its normal reset state. Latch 465 remains in a set condition for either two or four state times, depending on whether (1) one digit is to be loaded from R5 Register 34 into the Y input of adder 405 according to a 1R5 signal or (2) two digits from R5 Register 34 is to be loaded into the Y input of adder 405 according to a 2R5 signal.

The resetting of latch 465 back to its normal condition is effected by dual speed shift register 440, which is responsive to the outputs from NAND gates 461 and 468 for resetting latch 465 two or four state times after the conditions occurring at the aforementioned gates set the latch. Two speed shift register 440 normally requires four state times for a bit to cycle therethrough, except when the 1R5 signal is a logical zero indicating that only one four bit digit is to be shifted from R5 Register 34 into the Y input of adder 405, thus requiring that the latch to be reset after two state times.

Dual speed shift register 440 includes a NAND gate 470, a series of six inverters 471-476 and another NAND gate 477. The NAND gate 470, the inverters 471-476 and NAND a gate 477 are coupled in series with clocking gates 470a-476a disposed between adjacent stages. Gate 470a between NAND gate 470 and inverter 471 is clocked at φ1 and similarly gate 474a between inverters 474 and 475 is also clocked at φ1 while gate 472a between inverters 472 and 473 and gate 476a between inverter 476 and NAND gate 477 is selectively clockable at either φ1 or φ2. The other clocking gates 471a, 473a and 475a are clocked at P. As can be seen, if gates 472a and 476a are clocked at φ2 there is a two state time delay in dual speed shift register 440 whereas if gates 472a and 476a are clocked at φ1 there is a four state time delay. Gates 472a and 476a are selectively clocked at φ1 and φ2 depending upon the state of 1R5, gates 472a and 476a being clocked at φ2 when 1R5 is a logical zero and clocked at φ1 when 1R5 is a logical one. Thus, clocking gates 472a and 476a are responsive to φ2 when supplied via gate 441. Gate 441 is responsive to 1R5 inverter to true logic by inverter 442. Clocking gates 472a and 476a are also responsive to φ1 when supplied via gate 443. Gate 443 is controlled by inverter 444 which is responsive to the output of inverter 442.

SCAN GENERATOR COUNTER AND SEGMENT/KEYBOARD SCAN

The keyboard logic 35, display decoder 46, output register 47, state time generator 48, scan generator counter 36A and segment/keyboard scan 36B are depicted in FIG. 11. The scan generator counter 36A comprises a three-bit shift register, each stage which is comprised of inverters 501 and 502, the stages providing outputs U, U, V, V, W, and W. Scan generator counter 36A also includes a series of gates 508 which are responsive to the outputs of the inverters. The output of gates 508 is connected to the input of inverter 501 in the first stage of the counter. Inverters 501 and 502 in each stage are interconnected by gates 539 which are clocked at SOφ1 and the stages of the counter are interconnected by gates 540 clocked at S31P1. Thus, the number contained in scan generator counter 36A is undated once each instruction cycle. The number loaded in the counter is dictated by the pattern of feedback logic gates 508, which produces the output shown at reference A on FIG. 11. As can be seen, counter 36A does not "count" sequentially, but during eight instruction cycle provides the three bit binary representations of zero through seven.

Gates 508 comprise an AND gate 508a which is responsive to U and V outputs of counter 36A, an OR gate 508b responsive to the output of AND gate 508a and the W output from counter 36A, an OR gate 508c responsive to the U, V, and W outputs from counter 36A, and a NAND gate 508d which is responsive to the outputs of OR gates 508b and 508c. The state of counter 36A is initialized by a RESET signal on line 505 which inserts a logical one into the 501 gates of each stage of counter 36A. As can be seen from the table at reference A, on FIG. 11, counter 36A "counts" through the eight different possible binary stages producing the following sequence in binary: 7,6,5,2,4,C,1,3. It is only required that the counter count through the possible eight states; there is no requirement that the eight states be in any particular sequence. Counter 36A is a novel feature of this invention which derives such a non-sequential binary output.

Referring now to Table Va, there is listed the states through which counter 36a counts. As can be seen, all the bits are left shifted one bit and a new bit is inserted turning each incrementing cycle, that is, once each instruction cycle. A new bit is generated by feedback logic gates 508 or other such feedback logic means. The pattern of the gates 508 has been described for the three bit counter and may be derived by taking the available signals, i.e., the output of each stage and its inverse, and solving Kavnaugh equations for inserting a logical one into the least significant bit position of the next number to be generated in response to decoding an octal 6, 0, 1 or 3. Conversely, a zero is inserted into the least significant bit position of the next number to be generated when an octal 7, 5, 2 or 4 is decoded. Thus, the desired non-sequential pattern of states is generated.

Referring now to Table Vb, there is listed the states through which a four bit non-sequential counter would count, for example. Using a similar decoding scheme, that is, providing a pattern of gates similar to feedback logic gates 508 or other such feedback logic means, the outputs of the four stages and their inverses are used to provide a logical one in the least significant bit position of the next number to be generated in response to decoding a hexadecimal 0, 1, 3, 7, 14, 13, 12 or 2. The precise pattern of such gates is not shown in detail herein; however, the pattern may be derived by solving the Kavnaugh equations for the aforementioned logical conditions of the feedback logic. It should be evident, moreover, that the non-sequential counter scheme here disclosed is usable with counters having more than four stages.

The segment/keyboard scan 36B is provided by an eight stage shift counter which is arranged as a ring counter for shifting a logical zero to a different stage during each instruction cycle. Each of these stages comprises a pair of inverters, 509 and 510, except for the first stage which comprises a NAND gate 509a and an inverter 510. The first stage drives the D segments of the display. The NAND gate 509a is responsive to the output of inverter 510 in the last stage and to circuit ground clocked at S31φ1. The eight stages in segment/keyboard scan 36B are interconnected by gates 514 which are clocked at S 30P1. Segment/keyboard scan 36B is further interconnected with the RESET signal on line 505 for inserting a logical one into all stages of the counter, gates 511 being used for inserting the one's into the 509 inverters. Gate 511a inserts a zero into the 510 inverter of the first stage, which is equivalent to inserting a one into NAND gate 509a. The 509a NAND gate is responsive to gate 512 for inserting a zero into the first stage of segment/keyboard scan during the subsequent instruction cycle. The outputs from inverters 510 in each of the stages are connected to an output driver 513 whose output is connected to the pins labeled SEG A-SEG G and SEG P. Thus, one of the segment pins (SEG A-SEG G or SEG P) is enabled during each instruction cycle following the first instruction cycle. The segment drivers also serve as the strobing lines for strobing the keyboard as shown in FIG. 2.

The RESET signal is generated as is now explained. DISP, from decoder 209 (FIG. 8), is provided to a latch circuit comprised of inverters 503 and 504. The output of inverter 503, DISP, is supplied the input of an edge detecting circuit comprising an inverter 506 and a NAND gate 507. The edge detecting circuit senses a decoded display instruction for outputting RESET on line 505 to segment/keyboard scan 36B and scan generator counter 36A.

OR gate 515 is responsive to the DISP and REL HOLD signals. NAND gate 500 is responsive to the HOLD signal from NAND gate 219 (FIG. 8) and the output of OR gate 515. The output from NAND gate 500, HOLD, is supplied to the add-one circuit 119 in program counter 32A (FIG. 7). Gates 500 and 515 cooperate with add-one circuit 119 and program counter 32A to stop incrementing the number stored in program counter 32A when either the HOLD signal is generated by NAND gate 291 in response to a non-match between the contents of counter 284 and RAB 44 or upon the decoding of a display instruction until REL HOLD is generated. REL HOLD is generated by PLA 527 indicating that scan generator/counter 36A has cycled through the eight possible states thereof.

KEYBOARD LOGIC

Keyboard logic 35 comprises a decoder 517 which is driven by inverters 518 which are in turn connected by via buffers 516 to chip 10 pins (K1-K5) and conductors 16' (FIG. 2) of X/Y matrix keyboard 12. Inverters 518 normally provide a logical one output to decode 517 thus the outputs of the decoder 517 are normally at a logical zero. However, when a key is depressed while keyboard row conductors 14 are being scanned by the outputs occurring on SEG A-SEG P, a logical zero is outputted by one of the inverters 518 thus causing a binary representation of the particular one of five keyboard lines (K1-K5) to appear on the three output lines KR5-KR7 from decoder 517. At the same time the KEY DN (keydown) signal from decoder from 517 becomes a logical one, indicating that a key has been depressed. Thus, when the KR1-KR3 inputs to R5 Register 34 are loaded from the U-W outputs scan generator counter 36a, the KR5-KR7 inputs of R5 Register 34 are derived from the output of decoder 517, thereby producing a unique binary input on lines KR1-KR3 and KR5-KR7 for each key position of the X/Y matrix keyboard 12. The inputs to R5 Register 34 caused by keyboard logic 35 are listed in Table II. The KR1-KR3 and KR5-KR7 inputs to R5 Register 34 are inputted at S30P1 after a key is depressed while the calculator is in a display mode. NAND gate 519 is responsive to DISP, KRY DN and a S30φ1 clock; the output from NAND gate 519 is gated out at S30P1 via gate 520 providing the LOAD R5 signal to line 457 (FIG. 10) in R5 Register 34, thereby effecting the loading of R5 Register 34 with a number from lines KR1-KR3 and KR5-KR7 indicative of a particular key depressed during a display operation.

DISPLAY DECODER

Display decoder 46 receives a data representing numerals to be displayed from operational register A on line 549 and inverts the same by inverter 550. The data from operational register A is of course, in serial format and the least significant bit (in both true and false logic) is first loaded into the two input lines of programmable logic array (PLA) 521 at time P1 of an even state time (E.P1) via gates 522, the next least significant bit being loaded into two other inputs to PLA 521 via gates 523 at P2 of the same state time, the next bit being communicated at P1 of the next following odd state time (O.P1) to two more inputs to PLA 512 via gates 524 and the most significant bit of a digit being inputted into one input of PLA 512 at the next following P2.

Display decoder 46 is also responsive to the data from operational register B, which indicates where the decimal point is to be displayed among the numerals, whether minus signs are to be provided and which digits are to be blanked according to the codes listed in Table III, which are decoded by inverters 525, 547 and 548 and NOR gate 526 in combination with PLA's 521 and 527. As is shown in Table III, the least significant bit, which is a minus sign indicator, is clocked to inverter 525 via gate 528 at P1 of an even state time (E.P1). The output from inverter 525 is the false logic minus sign which is clocked at O.P2 and E.φ1 to PLA 521 and 527. A logical one in the second least significant bit of a digit from operational register B indicates that a decimal point is provided in that digit; this bit is clocked E.P2 via gate 529 and inverters 547 and 548 to PLA 527. A zero in the most significant bit of digit indicates that the digit is to be displayed (i.e. not blanked). This bit is communicated to NOR gate 526, which also receives a DISP signal rom decoder 209 (FIG. 8); this bit is clocked at P2 of odd state times, providing an ENABLE signal in true logic to PLA 527. Of course, if ENABLE is a logical zero, the associated digit position is blanked (with the exception of the decimal point segment). The outputs from PLA 521 are outputted during O.P2 and E.φ1; that is, after four bits of a serial data digit have been decoded in PLA 521, it is then clocked out to PLA 527. PLA 527 is also responsive to the U-W signals (indicating which segment is being scanned) provided by scan generator counter 36a and their inverses. Thus PLA 527 and 521 determine whether a logical one or a logical zero should be loaded into output register 47 for each digit received from operational registers A and B during the scan of a particular segment of the display. A logical one from PLA 527 loaded into a stage of output register 47 indicates that the particular character segment scanned by segment/keyboard scan 36b in the character position in the display corresponding to that stage of output register 47 should be actuated; a zero, on the other hand, indicates that the segment being scanned should not be actuated for the digit position corresponding to that stage. Decoder 529 "NANDS" the outputs of PLA 547 to provide twelve serial bits of data to a twelve bit shift register in output register 47.

Display decoder 46, being response to the contents of operation register A for the numeric information and the contents of register B for the display information, is a novel feature of this invention which reduces the amount of dedicated circuitry required for digit blanking, minus sign indication and decimal place indication. The disclosed system permits the contents of register B to be built up according to codes stored in the read-only-memory for providing the display information, thereby permitting greater flexibility in the numbers displayed. This simplifies, for example, the display of two separate numbers at the same time, one being on the right hand of the display, and the other being on the left hand side of the display and simplifies placing the negative sign adjacent to negative numbers displayed, as opposed to being on the left hand of the display as typically done in prior art display systems.

PLA 527 is also responsive to a decimal point blanking signal provided by an inverter 551 clocked at O.P2. Inverter 551 is responsive to the DISP signal from decoder 209 (FIG. 8). The ENABLE signal from NOR gate 526 is effective for disabling segments A-G of the display characters for blanking purposes. The decimal point blanking signal from inverter 551 is applied to a programmable gate 536 in decoder 527 for blanking the decimal point segment of the display. If programmable gate 536 is not programmed, then the decimal point segment in the display will actuate even when the calculator is in a nondisplaying (e.g., calculating) mode. This novel feature of the invention permits the decimal point segments of the display to appear to the operator of the electronic calculator to randomly light during calculations. This is particularly useful during long calculations, which require a second or more to accomplish, so as that the operator knows that some function is being performed and so to make the calculation time appear shorter. If the calculator is not implemented with long calculational programs, then gate 536 may be programmed to eliminate actuating the decimal point segments during calculations.

OUTPUT REGISTER

Output register 47 comprises a twelve stage shift register, each stage comprising a pair of inverters 530 and 531. Output register 47 is loaded once each instruction cycle from PLA 527 via decoder 529. During the first instruction cycle of a display cycle, the HOLD signal from NAND gate 500 inhibits incrementing of the program counter 32a, the D segments in the display are decoded by display decoder 46 and output register 47 is loaded with the codes for strobing the D segments of the display. Since the contents of output register 47 is not provided to the display until the following instruction cycle, keyboard/segment scan 36b is arranged to start scanning during the instruction cycle following the decoding of a display instruction. First the D segments are energized in appropriate digit positions for one instruction cycle, followed by the A segments during the next instruction cycle, followed by the B segments and so forth as the logical zero steps through keyboard/segment scan 36b.

The calculator clock (FIG. 3) is responsive to the decoding of a display instruction by decoder 209 (FIG. 8) for slowing down the clock during display operations. The clock must be slowed down during display operations if a VLED display is used because, given the time required to turn on a VLED, and the normal clock frequency of the calculator disclosed herein, the duty cycle of the display would be approximately 65%; however, with the normal clock frequency reduced by one-fourth, the duty cycle improves to approximately 95%. Even at this reduced speed the segments are scanned at a rate faster than that which the human eye may discern and therefore the segments appear to be constantly actuated. To make the display constantly actuated, a display instruction word is typically followed by a conditional branch instruction word to branch back to the address of the display instruction until the condition latch 41 has been set by a LOAD R5 signal indicating that the operator is inserting new data. Moreover, in the embodiment depicted herein, preferably two display destructions are used as a pair (as denoted by reference A in FIG. 11) because the keyboard line KS7 is not strobed until the first display cycle has been accomplished; recalling that the keyboard is responsive to an input only during a display cycle instruction as provided by NAND gate 519, the keyboard would not be sensitive to keys on the KS7 line unless two display instructions followed each other. Alternatively, of course, a trailing edge circuit could be built into the DISP signal applied to NAND gate 519 for delaying that signal one instruction.

Each of the inverters 531 in output register 47 is connected either to an inverter 533 or a NAND gate 534 or 535 via a gate 532 clocked at S30φ2. Inverters 533 and NAND gates 534 and 535 are precharged to V_(ss) at S30P1. The stage of output register 47 corresponding to the least significant digit (D1) is connected by a NAND gate 535 to a depletion mode device 537 for supplying a V_(DISP) voltage to the pin of chip 10 (D1/SEG P) which is connected to the common electrode of the display device in the least significant character position. NAND gate 535 is also interconnected with the output of the inverter 510 in the stage of segment/keyboard scan 36b corresponding to segment P. Further, the driver 513 corresponding to segment P is connected at its output to the depletion load device 537 corresponding to the least significant digit position of output register 47. This permits a reduction in the number of pins used on chip 10; however, then decimal point segment (segment P) may not be actuated in the least significant digit position. The interconnection between inverter 510 and NAND gate 535 assures that the current is not sourced and sinked at the same time at the D1/SEG P pin.

Similarly, the stage corresponding most significant digit (D12) in output register 47 is also interconnected via NAND gate 534 to its depletion load device 537, thereby permitting the connection of the D12 and segment D outputs to a common pin. Thus, NAND gate 534 is also responsive to an output from inverter 510 in the segment D stage of segment/keyboard scan 36b. The remaining digit positions in output register 47, D2-D11 are interconnected with the appropriate pins on chip 10 via inverters 533 and gates 532 interconnecting the outputs from inverters 531 with depletion load devices 537. Thus, for the D1 least significant character position all segments in the display except the P segment are energizable, for the D2-011 character positions all segments are energizable and for the D12 character position all segments except the D segment are energizable.

The outputs from NAND gates 534 and 535 and the output from inverters 533 are each provided to gates 538 in addition to gates 537. Gates 538 selectively interconnect the twelve display output pins (D1/SEG P-D12/SEG D) with feedback circuit 541. Feedback circuit 541 is connected with driver 513 in keyboard/segment scan 36B for maintaining a constant voltage across an actuated VLED.

STATE TIME GENERATOR

State time generator 48 is responsive to the calculator clocks φ1, φ2, and P2 for providing a binary representation of which one of the 32 state times of the calculator is on lines A-E in true logic and lines A-E in false logic. While state time generator 48 is shown here with five stages for counting 32 possible states, it soon will be seen that state time generator 48 is expandable and reduceable to count through 2N possible states where N is equal the number of stages in the state time generator.

The first stage of state time generator 48 comprises two inverters, 542a and 543a which are arranged in series with gate 544a, which is clocked at time φ2, forming a latch. The 543a gate provides the true logic A output and the output of the 542a gate provides the false logic A output. The output of gate 544a is connected by gate 545a to an inverter 551a. The output of inverter 551a is used to (1) provide a CARRY indication to the other stages of the state time generator 48 indicating a CARRY condition and (2) is clocked by gate 552a at time P2 back to the input of inverter 543a for changing the state of the latch. The aforementioned gates and inverters having an "a" subscript comprise the stage in state time generator 48 corresponding to the least significant bit. The stages in state time generator 48 corresponding to the more significant bits are identical to the aforementioned stage except that (1) the subscripts for the gate and inverter numbers are changed to correspond to the more significant bit outputs and (2) the output from inverter 551 is clocked to the input of inverter 543 at time P2 only if a CARRY signal, i.e., a logical one, occurs at the output of inverter (s) 551 in all the preceeding less significant bit stages. Thus, gate 552b is responsive to not only the P2 clock signal but also the output of inverter 551a which is supplied by an inverter 553a to a gate 554a. Similarly, gate 552c, in a third stage of state time generator 48, is responsive not only to the P2 clock signal, but also the outputs of inverters 551a and 551b via NAND gate 553b and gate 554b.

State time generator 48 operates as is now described. Assuming that state time generator 48 is at time 00011, then inverters 543a, 551a, 543b, 551b, 542c, 542d, and 542e are all outputting a logical one while inverters 542a, 542b, 543c, 551c, 543d, 551d, 543e, and 551e are all outputting a logical zero. At time P2, however inverter 551a inserts a logical one into inverter 543a, thus changing the output from 543a to a logical zero; inverter 551b, likewise inserts a logical one into inverter 543b because inverter 553a is outputting a logical zero, thereby causing gate 554a to conduct the P2 timing signal. Also, at the same time P2, inverter 551c inserts a logical zero into inverter 543c because the outputs from inverters 551a and 551b are both a logical one and the output from NAND gate 553b is a logical zero, thereby permitting gate 552c to conduct at time P2. Thus the C output becomes a logical one while the B and A outputs become logical zeros. The D and E outputs remain unchanged because NAND gate 553c and 553d both provide a logical one output, there being at least one logical zero input thereto, thus gate 554c and 554d will not conduct the P2 clock unless through to gates 552d and 552e.

As can be seen, state time generator 48 is easily expandable by providing additional stages of the type shown and described by conditionally clocking the P2 pulses to the 552 gates, condition being tested by a NAND gate 553 which is responsive to the outputs from inverters 551 in each of the less significant bit stages.

The outputs from the stages of the state time generator on lines A-E and A-E provided to a decoder 555 for providing outputs corresponding to the particular state times required by the logic circuitry shown in FIGS. 6-11. While state time generator decoder 555 is not shown with the gates being programmed, the gates would be programmed to provide indications of, for instance, the S₀, S₃₀, and S₃₁ state times required by the logic circuitry depicted in the FIGS. 7-11.

REGISTER CONFIGURATION

As has been previously discussed, the operational registers 38 and the storage registers 39 are generally comprised of long shift registers, the stages of which are of known design. It should be evident, however, that given the 0.625 microsecond basic clock frequency, that the shift registers of the operational registers 38 or storage registers 39 must be able to accommodate at a high bit rate and further must be able to clock one bit from one stage to a following stage in two clock cycles. While it is presently known how to implement a shift register being able to accommodate such clock rates on such a low number of clock cycles (for instance, R5 Register 34 is of such a design), the design of the stages in the operational registers 38 and storage 39 can be simplified if the bit rate were halved and there were four clock cycles to transfer a bit between adjacent stages. Referring now to FIG. 14, there is shown at 14(a) and 14(c) the operational and storage registers arranged as 60 and 512 bit shift register respectively. However, utilizing the register architecture depicted in FIGS. 14(b) and 14(d) permits four clock cycles to be used for transferring a bit between adjacent stages in a shift register at one half the speed of the registers depicted in FIGS. 14(a) and 14(c). The pairs of 30 bit and 256 bit shift registers of FIGS. 14(b) and 14(d) which have common outputs and inputs, are clocked on different phases of the same clock, i.e., one register of a pair may be clocked on a P1 clock while the other is clocked on a P2 clock conversely, one register of a pair may be clocked on a φ1 clock while the other is clocked on a φ2 clock. In any event, the outputs and inputs of a register pair tied in common with the intervening stages being of conventional design. Moreover, the data stream at the inputs and outputs of the register pairs of FIG. 14(b) and 14(d) are equivalent to that of FIG. 14(a) and 14(d) respectively. These pairs of registers is an important feature of this invention permitting the use of ordinary shift register stages in a shift register having a high bit rate and a low number of clock cycles to transfer a bit between stages thereof.

Having described the invention in connection with certain specific embodiments thereof, further modification may now suggest itself to those skilled in the art. It is to be understood that this invention is not limited to the specific embodiments disclosed, except as set forth in the appended claims.

                  TABLE I                                                          ______________________________________                                         INSTRUCTIONS:                                                                  ______________________________________                                         ______________________________________                                          Branch on condition - See FIG. 12(a). Program                                     counter branches to location defined by A field                                (10 bits) only if C bit is the same state as is                                COND in the condition latch.                                               2.  Branch Unconditionally (CALL) - See FIG. 12(b).                                Program counter branches to location defined by                                A field (11 bits). Incremented address being                                   branched from is stored in subroutine stack.                               3.  Branch to R5 - See FIG. 12(c). Program counter                                 branches to location defined by contents of R5                                 Register. Field Q is ignored.                                              4.  Return - See FIG. 12(d). Program counter branches                              to location defined by the last address to be stored                           in subroutine stack. Field Q is ignored.                                   5.  Operations under Mask Control - See FIG. 12(e)                                 MF - One of twelve masks. See FIG. 66.                                     J -    00     Operational Register A                                                  01     Operational Register B                                                  10     Operational Register C                                                  11     Operational Register D                                           K -    000    A is added to or substracted from contents of                                  register defined by J                                                   001    B is added to or substracted from contents of                                  register defined by J                                                   010    C is added to or substracted from contents of                                  register defined by J                                                   011    D is added to or substracted from contents of                                  register defined by J                                                   100    Decimal one is added to or substracted from                                    contents of register defined by J                                       101    Register defined by J is right on left shifted                                 one digit                                                               110    R5 (LSD) is added to, substracted from or                                      stored in the Register defined by J                                     111    R5 (both digits) is added to, substracted -  from or stored                    in the Register defined by J                                     L -    00     Arithmetic result to register defined by J                              01     Arithmetic result to register defined by                                       K(K=000-011 only)                                                       10     Arithmetic result                                                              suppressed (K=000-100 only) or shift                                           operation (K=101)                                                       11     See LN field explanation                                         N -    0      Add (Left Shift)                                                        1      Substract (Right Shift)                                          LN -   110    Register to A Register exchange (J=00 only).                                   Content of Register A is exchanged with con-                                   tents of an operational register defined by K                                  (K=000,001,010 or 011 only). Any exchange                                      instruction using a mask involving D.5 cannot                                  be followed by a register instruction using a                                  mask involving DO.                                               LN -   111    Register to Registor Store. Content of register                  (cont)    defined by K (K=000,001,010,011,110 or 111                                     only) is stored in register defined by J.                            111       If K is 100, decimal one is stored in LSD and                                   zero in all other digits in register defined                                   by J (mask control digits only effected).                           6.  Non-Mask Operations (misc). - See FIG. 12(f). Unless                           otherwise specified, instruction is not dependent on                           content of Q.                                                              P Field                                                                        0000      STYA - Contents of one Y group storage                                         register defined by RAB is loaded into                                         register A                                                           0001      NAB - 3 LSD of Q are stored in RAB                                   0010      See "branch to R5" location instruction                              0011      See "return" instruction                                             0100      STAX - Content of register A is loaded                                         into the X group storage register defined                                      by RAB                                                               0101      STAX - Contents of the X group storage                                         register defined by RAB is loaded into                                         Register A                                                           0110      STAY - Contents of Register A is loaded                                        into the Y group storage register defined                                      by RAB                                                               0111      DISP - Register A and Register B are out-                                      putted to the display decoder and the                                          keyboard is scanned. A closed keyboard                                         switch loads K5 and sets condition latch.                            1000      BCDS - BCD set - enables BCD corrector in                                      arithmetic unit                                                      1001      BCDR - BCD reset - disables BCD corrector                                      in arithmetic unit which then functions                                        hexadecimal.                                                         1010      RAB - LSD of R5 (3 bits) is stored in RAB                            1011-1111 Not Used                                                             7.  Non-Mask Operations (Flag Operations) - See FIG. 12(g)                         The Flag Operation - Toogle, set, reset and test - are                         performed by arithmetic unit on flag address in register                       J, digit D and bit B. Flag test sets the condition latch                       if the flag is set; otherwise the condition latch is not                       affected. Toggle flag changes 1 to 0 or 0 to 1.                                          REG.                                                             J -    00     A                                                                       01     B                                                                       10     C                                                                       11     D                                                                              DIGIT                                                            D -    01     D.sub.13                                                                10     D.sub.14                                                                11     D.sub.15                                                                       BIT                                                              B -    01     LSB                                                                     01     "                                                                       10     "                                                                       11     MSB                                                              F -    00     Set Flag                                                                01     Reset Flag                                                              10     Test Flag                                                               11     toggle Flag                                                      ______________________________________                                    

                  TABLE II                                                         ______________________________________                                          EIGHT BIT R5 REGISTER                                                          ##STR1##                                                                      ______________________________________                                         K         KEYBOARD LINE ACTUATED                                               001       K1                                                                   010       K2                                                                   011       K3                                                                   100       K4                                                                   101       K5                                                                   K         SEGMENT SCAN LINE ACTUATED                                           000       KS0           (SEG E)                                                001       KS1           (SEG F)                                                010       KS2           (SEG B)                                                011       KS3           (SEG G)                                                100       KS4           (SEG C)                                                101       KS5           (SEG A)                                                110       KS6           (SEG D/D12)                                            111       KS7           (SEG P/D1)                                             ______________________________________                                    

                  TABLE III.                                                       ______________________________________                                         REGISTER B                                                                     DIGIT CONTROL CODE                                                                             FUNCTION                                                       ______________________________________                                         1XXX            Display digit is blanked in the                                                corresponding digit position.                                  0XX1            Turns on minus sign (Segment G)                                                in corresponding digit position.                               XX1X            Turns on decimal point and digit                                               specified by register A in corre-                                              sponding digit position.                                       OXXO            Turns on digit specified by                                                    Register A in corresponding                                                    digit position.                                                ______________________________________                                    

    TABLE IV       INST.  WORD ADDRESS (FOR COLUMN) INSTRUCTION WORD (IN HEXADECIMAL) 0 IN      HEX) 0 1 2 3 4 5 6 7 8 9 A B C D E F 10        000 1213 1124 13E8 1B84 0CAE 1808 16B6 1606 1665 1B84 1124 0CAE 1EE1      140C 071E 1A8C 0A28 011 0509 198E 1949 19F5 1940 1AED 1B18 1A07 0CAE      1DA6 1126 19FB 1124 15FF 1B84 1124 1639 022 1B84 180A 18FA 0CAE 1D0C      1126 0C72 1E4F OC7AoC7D 1F83 0DA7 0C70 1A4F 0FE1 1A78 18A0 033 1AE7 18BB      0CAE 1C69 1124 1A75 1126 0CAE 1FAF 0C72 1E2B 0F27 1A22 0827 185C 187A      1AE4 044 18BC 1124 0CAE 1C96 1840 1126 0CAE 1FC5 0C72 1E56 0C93 1A5C      0CHD 1A8D 1A1B 1AEA 1A68 055 0CD8 1860 0CD8 18AB 1124 0CAE 1FC6 0CA6      1A8F 0C74 1A7D 0C28 0CAE 1A6F 0CDA 0CE0 18AE 066 1124 0C91 1B83 0CB2      186D 0C7A 19A8 1124 18FB 081F 08C1 140D 081F 0757 0E04 070E 1B84 077      130B 0D01 1884 1126 0CAE 1C84 0C75 0C72 1E22 0CB2 0CA5 1B88 0E03 140C      0701 0C7A 1889 088 0E04 08E0 08E0 0CEE 1890 0E00 0701 0E06 08E1 0E0A      0E05 0CEE 1E1B 1885 1534 1442 07D7 099 15AE 1589 0C7A 1F84 075F 15D0      1B84 1124 0C7A 1C04 1666 0CAE 1B84 0324 1F84 16B6 1600 0AA 1B84 0C24      0CAE 1A6F 0D1F 1126 140C 0C39 0C3D 0CE2 1C89 0C38 0CDA 1CB9 0C3C 1470      1B88 0BB 0CEC oCB2 1DA9 1124 1534 0CAE 18C3 0CA0 0C7A 18CA 0CE8 0CE2      18CA 0CAE 1C6F 08DF 0DFF 0CC 149E 0E08 0DDF 08FF 0F25 1A78 0CE2 18D6      0CA2 1C70 0C2E 1E78 0820 0C2A 18E1 0C2E 1CE1 0DD 0C26 0C24 18E3 0C23      0C2B 0CE4 0807 0E0A 1412 0717 07C7 0CE2 1CF8 0CEE 18F0 0CA2 1875 0EE      146C 1875 0CEA 18F3 0C38 0CA2 18F7 1601 18F8 15CE 146C 1A8D 0CAE 0CE0      18BB 1080 1400 0FF 1410 0A0D 1908 0A61 1416 0A60 1423 0A61 18FF 0AD9      1423 194D 1461 1080 1403 0A27 0C30 110 0C34 0A45 1908 0A60 1416 0A61      1423 0A60 190E 0C72 0E08 1910 1442 0C99 0717 15A1 0F4F 121 0E03 0CAE      1939 0CB2 1919 0CB2 0CA5 1921 0CA1 05E1 0A3F 0C7A 192F 0C2C 0CAE 1934      0F67 132 0C78 0F08 0AC7 1403 1423 0CA2 1D4D 0CA1 1400 1410 0A0D 1A1A      0A20 1947 1080 0CAE 1D29 143 1410 0CA1 0A21 1D4D 0E04 194D 0CAE 1F98      0CB2 1E1A 0E08 0CB0 1403 0A21 1D54 0220 1950 154 032D 0404 0328 195B      0E05 0A01 1947 16C3 07C7 0E09 1416 0F25 0C10 0C2E 1966 0C2D 0CED 165      04E70F67 0C78 0F09 0F25 197E 0CDC 0F08 1489 0F25 1981 071F 0425 0401      0501 132D 08C7 176 0CA0 0CA4 1DEF 0CDE 19EC 17E2 179A 1991 0F09 0F25      106C 0A1F 17A5 05FF 05E8 0C3E 198E 187 0C3A 0C36 198E 0C3A 0C32 1DCA      0F01 1572 05F8 071F 152A 0268 0268 0368 0368 0425 1D99 198 0467 0949      16C3 0368 0368 15B7 0CA2 1B88 0568 0CA6 1B88 0CA1 1465 1A36 1080 0CEC      0C88 1A9 0CA5 0CA0 0091 0C7A 19AF 00A7 0DA7 0C9C 0C94 0CAE 19B5 0DA0      0CE2 1DBB 0CEE 1D2A 0DA0 1BA 0DA0 0C98 192A 0CA2 1934 0CA1 0CBA 1DE0      0C2E 1D34 0D97 0F3F 00A5 1D34 0C2C 1934 0A27 1CB 0A20 0C34 0CF2 1DD2      0FE1 0C38 0F20 0CF6 1DD6 0F20 0CF9 0CFA 1DD9 0F20 0CA0 0CA4 0CEE 1DC      0CED 1982 04E7 1982 05DF 0A3F 0CB9 0C9A 1931 0C96 19E9 0C2C 1931      o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sD 1B5C 0968 0968 374 184B 0C32 0C33 0c36 0C35 1850      0E04 0E51 145 B 0E51 0E04 0E71 145E 0E61 0E04 0717 0CAA 385 0891 1ED6      1534 0CB6 1B8E 0CBE 0CBD 1F8E 0CB5 149E 0E09 0F25 0809 1E38 0CD9 0801      05E0 396 05E4 0F02 1124 0C7A 189E 1534 14421483 0C12 1BA1 08E7 0C91 1473      0C7A 1BA7 1483 1BA8 3A7 1486 1473 0C7A 1BAC 1486 1465 0D30 1BB4 1124      0CE4 140C 15F9 0E31 1450 146A 0E61 1467 388 13FB 0E71 1467 140D 0CE60CE7      1FB6 15AE 0E41 1467 0E51 1467 1B83 0CE0 1124 0C7A 18CA 3C9 0CB4 0E61      1412 1410 0CE2 1CA9 07C7 070F 1606 070E 1600 0E71 0747 1412 1500 070E      18A9 3DA 0757 0301 17CA 17C7 1700 17D5 17DD 17C7 179A 17D4 17D2 16C3      03C7 0300 0347 0300 0ED3 38B 07C7 15F9 0749 0067 0807 0E03 0000 0000      0000 0000 0000 0000 0000 0000 0000 0000 0000 3FC 0000 0000 0000 0000      0A67 0F60 1BF9 1410 0A47 0701 0E03 0F1F 0EDA 01C7 0E05 0E03 07C7 40D      0E41 1B0A 07C7 0B51 180A 0CE6 1C58 0F00 185F 0CDD 1824 0CDE 1821 0A1F      0D65 1826 0E06 41E 024F 0A7F 0B03 0AC7 181E 0CDC 0A4F 027F 0D49 0A0F      1432 0861 1C18 1572 0577 0128 0D60 42E 0508 1C1D 1829 0A00 0C3A 183D      0C36 183D 0825 1C3D 0C2A 1FF9 0F20 0801 0847 0F07 0E0A 440 0EAD 0E03      044C 0CA5 0C71 0001 1C49 0C14 1500 026D 0467 0460 0268 0061 1C56 004C      1C54 451 0061 19A1 0C10 0228 184C 0268 15BD 0065 1C56 19A1 0E05 0E61      0747 0E05 070E 0E03 1531 462 0A20 0C3E 1861 08DF 0E03 07C7 1412 071F      0F0F 15CE 0CE6 1C70 0Bo6 1871 0E04 071F 0E03 473 07D7 15AE 1589 071E      075F 15CC 071E 0749 0C54 0C58 070D 0C54 0567 0F0F 0C3B 1AAA 15BD 484      15BD 19A1 15C5 15C5 19A1 0C2A 1897 0C36 1CAF 0C32 1C97 0F21 0820 0C2E      18BE 0C36 1C97 495 0F01 0A2D 0E03 0A01 0E04 0C74 0CBD 0CB5 031F 0C78      0CAD 0CBE 0CB6 1CC5 03CF 0E07 4A6 0E07 1CA5 1525 0E07 0E07 18A8 043F      1489 152E 0E07 0E07 18A8 05FF 0C3A 0F25 1D33 0825 487 1933 0C32 18A0      0C36 1D33 0CAF 18A1 0820 0C2E 1C96 0F20 0F20 0F20 18BE 03C7 0E09 0CB6      4CB 1CDE 0C76 1C98 0E07 0E07 18DE 0A3F 0C36 0C3A 1CDE 0820 0C2F 18D7      0821 18FC 0820 0C22 4D9 0026 1CDE 0C2A 18DE 1461 1410 0A20 0A21 1432      0C76 1C98 0861 1CE9 0128 18E5 0F25 4EA 1CFC 0C2E 18EF 0C2D 0C78 1572      0D3F 0067 0C58 0D09 0D25 0D07 1CFC 0F37 0D09 0D25 1913 4FB 0CAC 031F      157C 05FF 0825 1D33 1489 0E25 1933 0CAE 0C7A 1D08 1388 1119 0C7A 1D0D      031F 50C 1320 0CAE 1D10 1357 08E7 0CEC 1070 08D9 0891 0C12 1D19 0D21      08A7 0C1A 191C 0CE0 0C16 51D1D1F 0CEC 0C7A 1922 0CE8 071F 1119 10D6 0C76      1931 0A20 0C32 192E 0349 0E08 0361 1D31 52E 0E09 035F 0E08 0E07 0E07      0E03 0E08 15A1 OE41 145D 0749 0C54 1576 0709 0C12 193F 0D67 53F 0847      0C7E 1D48 05C7 03E0 03E0 03ED 05E5 1D80 0CD4 0821 1574 1574 0C2F 1948      0404 1961 550 1575 02C7 0220 04E4 1957 02ED 1953 02E5 1962 0221 03C7      0717 1588 0324 1936 031F 1962 561 1575 0865 1968 0425 1968 0465 1D61      0228 0268 0CDG 197A 0C16 1978 0460 0CD2 1973 0C13 572 0F07 0E03 0821      022D 076D 0C50 0C5C 0E03 0561 0461 0A07 0E03 15BD 022D 0C16 1D7E 0525      583 1D49 15C4 0821 1982 0801 1982 0716 0349 0C61 03AD 15C5 0C1A 1D9C      0368 0265 1D94 0C60 594 1597 0228 198D 0215 1DCB 0211 0360 1997 158D      03A8 0C16 1DA1 1597 0C39 0025 1949 0228 5A5 15C5 0225 19AS 0701 0C3A      0C39 1FA6 0787 19CD 14ED 030F 0D01 0501 0C3A 19A2 0547 0849 5B6 0501      0561 1FA6 032D 1987 0201 0027 0C16 1BE6 0521 0525 19C3 0C15 0B03 026D      0C16 1FF6 5C7 0521 19C3 0527 0C14 0E03 0C38 070E 0C3A 19D1 0C13 058F      0C39 0C56 1DEE 0C16 0513 1DF3 5D8 05A5 18CD 0791 0C12 19E4 0C52 1DE6      0200 1DCD 0209 075F 19A1 0C52 1DDF 0208 141C 022D 5E9 036D 15AC 0324      1DE2 1A1C 0C16 19CD 0513 1DCD 05A5 0265 1DDA 022D 158D 1901 0C38 075F      5FA 1AC1 15AF 0517 0C52 19A1 13ED 0C38 0C3A 1A06 0225 1FF0 0C17 078F      0247 0D0A 0C11 0052 60B 1A0D 0C10 0C91 0D12 0C96 1B26 0508 1FE8 0201      0591 0549 15C0 02A5 1DE2 0C3A 1E2E 0220 61C 04A1 19E6 02AD 02A5 1D82      0065 1A1B 036815C5 1A1C050D 1A2A 0C17 05DE 0509 1A13 0389 62D 0220 038D      1A2C 0025 19E2 036D 0228 0225 1A2E 15C5 1A2E 1501 17E7 0701 02A5 1DA1      13ED 63E 05A1 1E48 05A1 1E44 0520      A3E 0C96 1A47 0520 0260 0C91 0849 0507 0978 0501 0591 1A5E 64F 036D 032D      1A5D 0381 0381 0308 0385 1A52 0309 0312 1A5A 00A5 1A4F 03A8 036D 0365      1A53 660 1580 0D17 094F 053F 19E2 0C30 0C32 1EAD 17F7 0587 0501 0C10      0225 1FE9 1584 0349 0C32 671 1A75 0067 0225 1DFB 031E 0301 080F 0821      1EC6 0821 1ED0 0821 1ED7 0821 1EDC 0027 17A1 682 031E 0C32 1A90 031D      1E95 0319 028F 0216 17A1 0216 0250 1A85 0217 0358 0287 17A1 0216 693      0212 1A8E 0860 02ED 02E5 1A75 0C32 1DFB 1687 07C7 0209 1580 071E 0C96      1AA3 0C10 0767 6A4 0597 007F 05AD 026D 0597 007E 070E 1601 19D1 1686      1589 0D00 0C62 1FEA 0DD9 08D9 058F 6B5 1A6E 0747 0701 17D7 17D5 0328      17D7 17DD 17C7 17D0 0328 17DD 17D5 0328 0328 0328 0E03 6C6 17CF 17D5      179A 0328 179A 17CA 17DD 17C7 1603 1A82 170C 17D0 0328 17D5 17D5 0328      1ACD 6D7 1708 17D0 16C3 1707 1ACE 17DA 17D0 16C2 1A82 1124 08FF 0C75      0C7A 1F52 0C3F 17A7 13D8 6E8 03CC 1589 1776 1584 13DA 0300 0C12 1AF1      0313 0D01 13DB 038D 0355 1EF9 0CA3 0C36 1807 6F9 0385 IBFF 0381 0C36      1AFF 0C13 0C32 0F25 1B40038D 1F07 0313 0C13 0CA3 039D 1F04 0353 70A 0C36      0317 0DC7 031E 0349 0391 00A7 0C7A 1815 17851B16 17AD 03C5 1F27 03C3      031E 0C7A 71B 1821 17A1 0312 1785 030A 1811 17A0 0308 030F 17A1 0381      1811 1B11 02E5 1811 030F 0C3A 72C 1832 0C7A 1831 13DA 0353 0316 15B0      156F 0C74 1F66 0716 1580 0757 1600 0C11 156F 0C36 73D 1846 13EB 0C35      1638 15FF 0C76 1846 15A8OCD1 0CD- 0CA2 1844 0CD0 08DF 0F7F 1384 038D 74E      1F50 0313 0353 1807 1776 0DC7 0C36 1F5C 13EB 15D0 1639 0C76 1F63 1600      0C16 0225 1861 75F 15FF 0C38 15B4 180D 128D 0C7A 184A 0C32 186D 13DA      15AF 0757 15D0 0C1 0787 0CA2 1874 770 13DB 0D01 0757 15D1 17A7 1B4A 0291      03AB 0390 02A5 1DAC 0C1A 19AC 0C32 1B84 0701 0C19 781 0CDA 19AC 0C18      19AC 0301 080F 0821 1F92 0821 1F9C 0027 0821 1BA1 1709 17DD 17CC 1BCA      792 17DC 17CC 1707 17CD 1700 17D7 17D2 17DD 0328 1BE6 17DA 17CC 1899      0317 080F 032D 7A3 0821 1BA2 0820 0E03 1572 087F 140C 092D 080E 0A28      0CBE 1F8E 0C6A 1C71 17D0 17CA 17D7 7B4 17CF 17C9 17CF 179A 1705 0D01      0328 179A 0757 1A01 1704 17CC 179A 17DD 17C9 17D7 17D5 7C5 17CA 1BB9      0328 18DF 17CA 0328 1BE0 1700 0328 1BE1 17DD 0328 1BE2 0328 1BE3 170D      0328 7D6 1BF4 0328 1BES 170D 17DD 17DD 17DD 0328 0320 0320 0320 0320      0320 0320 0320 0320 0520 7E7 19C3 0C16 0301 1FEE 0321 0C15 1FF4 0521      1FF3 0265 0D0F 1BE9 0027 0C74 19A1 0C3A 0C12 7F8 1BFA 0C74 0E03 0000      0000 0000 0000 00000000 0000 0000 0000 0000 0000 0000 0000 0000

                  TABLE Va                                                         ______________________________________                                         111                                                                            110                                                                            101                                                                            010                                                                            100                                                                            000                                                                            001                                                                            011                                                                            ______________________________________                                    

                  TABLE Vb                                                         ______________________________________                                         1111                                                                           1110                                                                           1101                                                                           1011                                                                           0110                                                                           1100                                                                           1001                                                                           0010                                                                           0101                                                                           1010                                                                           0100                                                                           1000                                                                           0000                                                                           0001                                                                           0011                                                                           0111                                                                           ______________________________________                                     

What is claimed is:
 1. A state time counter for a microprocessor system, said counter being responsive to a clock in said microprocessor system for counting state times, said counter comprising:(a) a plurality of latches for storing bits providing a binary representation of the state time the microprocessor system is in, each one of said latches including a pair of first inverters and means coupling said pair of first inverters in series; (b) a plurality of second inverters, each of said second inverters being coupled at the inputs thereof to an output of one of the inverters in said pair of first inverters, said second inverters outputting a carry control signal; (c) a plurality of transistors, each one of said transistors coupling the output of one of said plurality of second inverters to the input of the other inverter in one of said pairs of first inverters; (d) means coupling said clock to the control element of the one of said plurality of transistors coupled to the other inverter in said pair of first inverters forming the latch storing the least significant bit of the state time in said microprocessor system for changing the state of the latch storing the least significant bit in response to said clock; (e) means coupling said clock and selected ones of said carry control signals to each of said plurality of transistors coupled to the other inverter in said pairs of first inverters forming the latches storing bits more significant than said least significant bit for changing the state of the latches storing bits more significant than the least significant bit in response to the carry control signal outputted from all second inverters associated with latches storing bits less significant than the latch to be switched being of a preselected state and further in response to said clock. 